A Treatise Concerning Card Design in Infinity Wars and Speculating How Set Releases Ought to Proceed in the Future, Concluding with a Few Suggestions for Moving Forward
Concerning Design Space
Based off of any given game's mechanics, there is a finite amount of design space within that game. Designs can push the envelope, seek out and probe the edges of healthy gameplay and interaction with the rules, but eventually there are only so many stats and abilities you can come up with before you've exhausted every opportunity and the only thing left is to make things that are strictly better than their earlier counterparts.
Design space is limited within any one particular faction based off of its themes. You can't very well start giving the Overseers RNG effects, or the Sleepers flying, or the Warpath reanimation, because that's not how those factions are meant to work. Each faction has themes and mechanics which are specific to it--perhaps overlapping with another faction in part, but each has its own synergies which that faction does best--and things that it's not supposed to be able to deal with. You cannot bleed too many cards between these factions' themes/identities before they begin to lose their identities and render the faction system meaningless. If every faction in the game had the same cards, the only reason to play one over the other would be aesthetic. Worse, you could combine the best cards from multiple factions to create a redundant, incredibly consistent, powerhouse deck.
If you want to allow power creep and say "we're running short on new ideas, but here's a Better Paladin--7/7 2 cost charge cannot be killed by non-damage sources," you can but then your game will spiral out of control and just turn into a mess. Just look at Konami. They've let power creep get wildly out of hand and now constantly have to ban broken cards (or un-ban broken cards) in order to try and keep a semblance of balance (they also have something like Tier -1 decks and loads of turn 1 kills, so... not an example to emulate).
Eventually, your design space will run out. You can sort of see this already with the Flame Dawn. There aren't really too many more ways you can make 2-drops with charge anymore. A Flame Dawn rush deck is going to be as rushy and tempo-y as it'll get, and adding in new cards can only happen if they're better than older ones--creepier, as it were. While not completely exhausted, the Flame Dawn's nearing the end of its low-drop design space, and even if you come up with ideas for higher drops they'll never be played over the rush strategy and will be more or less pointless. Unless, I suppose, you make their late drops so good that Flame Dawn lategame becomes more viable than Flame Dawn rush, at which point you've crept in a completely different direction and left the Flame Dawn's particular style of rush-oriented gameplay behind. This is a faction that doesn't care about the late game because it wants to have won by then, and right now it's approaching a critical mass of early rush cards that can't be added to further without making cards that won't see play or cards that are creeping ahead.
Balancing tcgs is hard, as you can see. But y'all know this. The balance team certainly is aware of the fact. So what can be done?
Concerning Methods for Conserving, Reopening, or Recycling Design Space
The factions are getting cramped. They're running out of room and it's hard to come up with new ideas for new cards. How might one avoid falling into power creep but still make room for new sets of cards (gotta sell boosters, and nothing sells boosters like preordering a new set)? Not printing new cards is obviously out of the question, so how should we move forward?
Rotation. This has been mentioned before and it's one thought. Rotate out certain sets or certain factions from the game, allowing them in Infinite Mode but not in Ranked, Tournaments, or even Draft. This opens up functional reprints or near-reprints that maintain the standard metagame without tipping it over the edge, without unduly harming the Infinite Mode. However, rotation leaves a bad taste in folks' mouths. They don't like it. It's annoying. And IW's factions don't exactly map directly onto MtG's colors, so the textbook example isn't truly easily applicable to the situation (factions have far narrower and less flexible identities, while colors are broader, allow a variety of playstyles, and can rebrand themselves to a degree with each new world MtG visits--compare UB in Innistrad and UB in Kaladesh). While floated a few years ago by LM, it appears that faction rotation has been abandoned and Yodomare doesn't seem eager to pick it back up.
Let power creep happen. Honestly, not an amenable option, and to be avoided at all costs.
Stop making new cards. Definitely not an option, but I'd consider it preferable to rampant power creep.
Introduce a new faction. In theory, this will open up new design space and viola! More room for cards. Except, adding another faction means it needs a satisfactory base to work from, so plenty of cards when it's first released and more with subsequent sets. And with 100 card sets it's already split in enough ways between the 8 existing factions and Factionless--and the Sleepers have only been getting 1 or 2 cards per set for the last few sets! People love factions and want for there to be new ones though, so this is important to keep in mind. The earlier idea of rotation was designed to take factions out so more could be added in.
Release more promotional content, like Omni, Star Trek, and the proposed CDC Packs. It doesn't affect ranked, but it's fun and at least some people will buy into it.
It's late and I don't feel like being exhaustive right now (feel free to come up with more ideas, discussion is what I'm aiming for), so I'll just move on.
Concerning a Path Forward
New sets will come out (along with new alt-arts). I don't think continuing with business as usual will work for much longer, so here's my suggestion.
From here on out, sets will be 100 cards, as per usual. ~80 of those cards will be for a new faction release. Factions right now have about 90 cards, so theoretically an 80-card faction would start out even with its predecessors in terms of deckbuilding options and versatility, as well as draft variety. The rest of the set would be composed of one or two cards for each other faction, perhaps hybrids or mercenaries, with one or two factionless. Ideally, these cards would interact with the new faction's mechanics/design space from the lens of the older factions, perhaps offering counterplay or synergies.
This would 1) introduce new factions, something players want, 2) slow down the consumption of present available design space while opening up new space, and 3) not introduce undue/avoidable levels of power creep, assuming the new faction is properly balanced on release (looking at you, Overseers).
The downside, of course, is that we'd see fewer new cards for our favorite factions. Moreover, since these new factions would be confined in their vast majority to a single set (with a few cards coming out in each new set), faction packs for them likely wouldn't sell very well, since their normal set pack is basically (but not exactly) a faction pack. Even with the introduction of new factions, there's only so much design space out there. You'll still run out eventually (though hopefully many, many years down the line). And I guess Enyah becomes more powerful (if you're worried about that).
Those are my thoughts for now, though I'll certainly keep developing the ideas in the future. Thoughts? Discussions? I'm interested to see what you think.
TL;DR: Design space is limited, so just release new factions wholesale instead of trying to expand each of our current factions. Discuss.