Another interesting evolution pattern I’d like to see is smart zombies.
Have late-game zombies start to adapt human intellect and become smart enough to wield guns, weapons, etc. (goo ganados).
Would be cool to also have animal and some “failed” smart zombies turn into hideous monstrosities where the goo just goes nuts and turns zombies into lovecraftian/demonic mashups.
Fungal Smoker Feral Antlered Skeletal Hulk Zombie would be cool.
Maybe add a mechanic where instead of evolving into specific zombie types, the zombies acquire characteristics and traits of types over time (much like PC mutations), turning them into unpredictable modular killing machines.
Exposition to labs, radiation and otherwordly stuff, as well as fungi, insectoid and triffid locations would dictate what traits they acquire.
I understand this would require a lot of rewriting though. Would be nice nonetheless.
Both these ideas could also be toggleable, so people who want classic gameplay, smart zombies or mutant debles can chose their treats.