I don’t think the game has ever been about a “basic zombie infestation” - I’ve been playing from early on, and most of my memorable experiences have been about tirffids, graboids, fungals, giant bugs, mutants, cyborgs, strange things deep in labs, etc. and so on and so on.
The zombies have always been the sort of “basic introductory first experience”, in my experience, the main feature they possessed simply being the fact that they were common.
The vast majority of enemy types in the game, for the longest time and well into the old versions of the , have been “not zombies”.
Making the game even slowly switch from the starting survive in cities infested with zombies and trying to bring some sort of hope back into your world and fellow survivors (which I assume would be working by the time lore even becomes a significant in game play) to some sort of laughably fail to protect the small remaining sanity of the world as everything irremediably turns into a mockery of its former self is very prone to turn off a lot of possible gamers ( I for one know that it would turn me off from the game if it happened to me in my first plays) and its IMO just plain bad game design to introduce such strong genre changes halfway into the game. What would you do if you were playing say Red Dead Redemption and the game suddenly changed into the modern age? At least I know that I would throw my controller at the screen and then start playing again the parts that are not GTAIV.
You mean like a game of D&D where in the beginning you're fighting bands of goblins and kobolds in little camps or abandoned mines, and by the end you're fighting dragons, demigods and planeswalkers? There's a progression, and the world changes, but that doesn't mean the core theme of the game, whether "go on adventures and fight stuff to gain loot and experience" or "survive in a hostile world where everything seems to want you dead", is changing. Cataclysm's genre, or the closest thing it has to one, has always been a combination of horror/survival, exploration/discovery, and rebuilding/improving(both the players surroundings and themselves).
So you could argue the setting will be changing, but settings changing gradually over time is actually really common in games and is not something that tends to turn players off. Heck, take a mainstream game like Halo: it is fucking huge, and that starts out as a very different game (setting-wise) than it ends as, even within the first game taken by itself. The setting change isn’t anything I’ve ever heard people complain about (though they may talk about certain bits of it).
So yes, this would mean the setting would change a bit, slowly, gradually, in certain limited areas, but there is nothing genre changing about the changes discussed here, because the genre has never in any way been “zombies!” (unless you play classic zombie mode, of course, where this wouldn’t happen), it’s always been “everything that can go wrong is going wrong and all the disasters are true!” I’m of the opinion you’d get a game much truer to the Cataclysm by removing the zombies than you would by removing the not-zombies. (Luckily, there is no reason to remove either, as the zombies definitely have their place)
Personally, I am definitely not aiming for “some sort of laughably fail to protect the small remaining sanity of the world as everything irremediably turns into a mockery of its former self” - I definitely want the player to be able to rebuild and carve a place for themselves, and eventually their followers, in this new world. But it should require the player to change and adapt to do so. You may have noticed that cybernetics and mutations play a core role in advanced gameplay - this sort of theme, where this is a new world and the best way to survive is to become a new man, is something I definitely want to continue.
Especially since none of the non-zombie creatures are even all that insane. Certainly nothing Cthulhu level going on here, or even D&D level - hell, for how disturbing the nether creatures can be, they are incredibly mortal and less than supernatural in many ways: note that they are so weak they can’t even survive in our environment with the shielding embrace of human flesh! The Lacerated Skinwalker, for example, dies shortly after it appears, without the players input.
It’s more like an invasive species finding it’s niche, and the local ecosystem changing to accomodate it. When aa patch of barren and burnt ground turns into a field, does it become a mockery of what was there before? When that field is eventually reclaimed and turns into a forest, is that a mockery?
A big part of what I’d like to see late game is how the player and various NPC groups adapt and change to deal with these invasive species, how they create their own niche in this new forest. Some end up living with the fungus, finding a way to not only survive but thrive within its confines, much like the Forest People in Nausicaa. Some will augment themselves, consolidating and building upon the science we had previously to adapt it and maintaining something vaguely similar to what we had before through overwhelming power. Others may simply attempt to distance themselves and hide, others may give in, becoming mutated creatures able to operate effectively as true denizens of this new world.
But the game has always been about a lot more than zombies, and I see no reason why would should allow the mere existence of zombies and the fact that some people insist on seeing the game as nothing but a zombie simulator (despite extensive and overwhelming evidence to the contrary) prevent us from making a game that expands upon and digs deeper into the variety of themes that already exist.