Gamer ADD - the kitschy term used to summarize the general phenomenon of wargamers switching factions/game systems constantly, hereafter "GADD" - is a funny thing. Like most greed based desires, you can't satisfy it or make it go away by giving in to it.
If you do, what usually happens is that you buy all the models that you've had a fancy for, and use each of them once or twice. Then eventually you look around at your empire of models you use very infrequently and decide that you need to trim down; simplify your wargaming life. After a few weeks/months/years you manage to whittle your collection down to the bare essentials...which just so happens to give you a lot of room for new models, so why not branch out a little bit? Time is a flat circle, the cycle repeats, etc.
I've fallen victim to this cycle a number of times. When I worked for Games Workshop the (at the time) phenomenal discounts combined with most of my pay being disposable income combined into a firestorm of buying way, way, way too many models. I'm reasonably sure at one point I owned enough stuff to run (again, at the time) a 2,000 point army of 10 or so different armies across Warhammer: Fantasy and Warhammer: 40K. I needed shelves just to store all of the unopened boxes. Looking back on it, it was madness, but at least I was able to sell pretty much all of it over the years for a decent profit.
When I got into Warmachine, I decided to focus primarily on Khador. I bought everything I could, branching out very, very little (it took me awhile before I started picking up any Mercenary models, and I've only recently incorporated Mercenary units into my collection.) When Hordes came out I saw it as a great excuse to buy a second faction - it's a whole "new" game system, so why not jump in? I collected Legion of Everblight in the same way as Khador: everything gets purchased, no exceptions.
Again, looking back on it, that "collectivitis" is another kind of sickness; a lower impact version buying multiple factions. Instead of committing to a smaller pool of models and branching out when it made sense, I bought absolutely everything on the off chance I'd want to use it. The result ended up being that my Khador collection is massive, and while I use a good portion of it, there's definitely a chunk I wouldn't miss if it was gone. My Legion army was even worse: the pile of models was so big and full of stuff I either didn't like or wasn't interested in that when it came time to start painting that army, I decided it was ultimately better to just sell it rather than slog through dozens of models I didn't like (the actual reasons for selling my Legion collection were a little more complicated than that, but I would have been much less likely to sell it if the collection was less unwieldy and more focused on my interests in the faction.)
Remember what I said before: feeding the desire doesn't satisfy it. In addition to having collectivitis with Khador and Legion, I branched out into other factions a few times ("gamer ADD" flaring up again,) buying Cygnar, Trollbloods, and Skorne in sizable quantities. All of those armies were eventually sold or traded after minimal use, representing a waste of time and money with a very minor payout in terms of tabletop fun or hobby enjoyment.
I fell victim to this with Kickstarter as well. I bought into the Relic Knights Kickstarter, but instead of doing something reasonable like buying one, maybe two factions, I bought in for four. Four factions. For a game that, as neat as it looks and seems to play, is a game that my play group isn't going to tap into that much, and is competing for table time against plenty of other games.
Even now I'm still fighting that odd urge to branch out, to acquire more stuff. I still have my Khador collection - I'm keeping that until the models wither and crumble in my hands - and I started a slow grow Retribution of Scryah collection. I'm trying a different approach with Retribution: I'm building lists that I like, then buying the components. If a model doesn't end up in a list I like, I'm not buying it. Also: I'm painting everything before I'll let myself play it (with very few exceptions,) so my acquisition of models is slow and steady instead of gorging myself on the faction all at once like I have in the past.
So far, the experiment has been very successful. Knowing that I need to paint things before I can use them makes me very hesitant to buy more than one thing at a time, which keeps me from overloading on models and building a wall I'll never feel like chipping through. It also makes it a lot more satisfying to actually get the army on the table; I'm playing Retribution not just for the rules (in my experience, the primary motivator for GADD,) but also for the aesthetics. I really like the paint scheme I've come up with for Retribution, so I'm excited to grow the army not just to add new elements to it, but to add visual diversity and dimension to it as well.
GADD never really goes away though. It always lurks in a corner of your mind, waiting for you to become complacent so it can once again whisper sweet temptations into your ear. Khador has been in a mostly "finished" state for me for awhile - almost everything I own is painted, and there are few lists I want to run that I don't have the models for - and Retribution is slowly growing up at my own pace.
That leaves a window open; a window for another faction to sneak in.
A week or so ago I was musing about the possibility of starting up Skorne (again, though I barely played them originally.) This was the GADD talking: although Skorne has plenty of cool things going for it (some of the hardest hitting power out there and some of the best medium based infantry,) I'm not really interested in playing Skorne; more the novelty of playing Skorne. I'm sure I'd enjoy it for a little while, but inevitably I'd rotate back to Khador and Retribution, leaving Skorne sitting on the shelf at best or on the auction block at worst.
A friend of mine has started up Convergence of Cyriss (two friends have actually, but one more recently and more...zealously) and we've been talking about list ideas and different build paradigms. That of course got the gears turning (har har) and sure enough I came up with at least one Convergence list that I'd really enjoy running. It also would be pretty easy to put together and paint! What a deal!
This one is harder to resist because Convergence offers something that Khador and Retribution don't: the ability to run a crapton of warjacks, and do it well. That's something you usually have to go to Hordes for, and unfortunately for me I don't really like the design of any of the Hordes armies (or rather, I don't like any of them enough to be excited about painting them up.) I'm also not a massive fan of the design of the Convergence army, but I find it more palatable and workable than the Hordes armies (least of which because painting them up just in the default paint scheme would be hilariously quick and easy.)
PP also made this faction really easy to buy into by making it a "limited" release. Instead of buying into a new faction that will be expanded whenever a new book comes out, you've got what you have in the Forces of book, and any new releases will come at their discretion. It makes it much easier to alleviate concerns that you'll end up buying a ton of models for this new faction, because you can only really buy so much.
I still have my weak moments with Convergence (what long time Warmachine player wouldn't be interested in a faction that plays the way we thought they all would?) but I'm staying strong against buying in by reminding myself that it's fundamentally similar to Skorne: I'm only really interested in the novelty of the faction. I don't love the aesthetics, nor am I inspired to try something different when it comes time to paint them (which is what ultimately made me like my Retribution army so much.) Once the novelty of the few lists I buy wears off, it'll probably go back on the shelf or the auction block, just like Skorne would have.
The fine fellows at the "Troll Patrol" podcast pretty much nail the concept in their 6th episode: pretty much all of the Warmachine factions have grown to the point that you can play a ton of different styles of lists without having to step out of faction. Buying into a new faction because it offers some possible playstyle differences is absolutely tempting, but in the end (at least for me) it all comes down to how much I like the models and how much I'll want to paint what I buy. I got into this hobby for all aspects of it, and I really don't like buying models anymore that I know I'll never want to paint.
So while Skorne may be tempting for killer heavies and good medium based infantry, there are some list builds in Khador that can get me close to that (kinda sorta) that I'd be better off exploring instead of buying into a new faction. Convergence may have fantastic warjacks and warjack support, but Retribution has (at least in the Vyre warjacks) very interesting, flexible warjack models that are a positive delight to use after fussing with Khador's warjacks for years. Retribution even has 'casters that make running warjack heavier lists possible in the Vyros', and he's going to be a lot more fun to run once Imperatus comes out.
While all of those options invariably involve buying more models for the factions I play, it's a much more reasonable investment than buying into an entirely new faction (which seems to run around $200-300 on average for a 50 point army based on my wandering eyes.) And it has the benefit of offering me more general options in the factions I already own, instead of giving me an autonomous chunk of models that I either need to invest more into, or break out only occasionally.
To be clear: I'm not saying that there's anything wrong with owning multiple factions, or picking up a small force of another faction on the side. The Syntherion theme list I came up with is so sexy, it's going to be hard to resist that forever. But having gone down the rabbit hole of buying stuff I never really ended up using many times, I've learned that it's very important to sit down and ask yourself: "Why am I interested in this?" Sit down and try to evaluate if you're really interested in the new hobby expansion, or if you're just buying it because it's cool and "I'll probably use it eventually." At least in my experience, being able to make that distinction will save you a lot of time and money in the long run.
Now if you'll excuse me, I need to figure out a way to configure my browser so that it crashes if I try to add Convergence models to any of the shopping carts for the online stores I frequent. Just to be safe.