slippery slope arguments dont work as like, all those people you listed are you know, people. who go to zoos and are players of the game. not ridiculous why ever would anyone want things.Like existence of disabled people isn't a tricky subject it's just reality. erasure of them in media is a tricky subject and thats the thing accepted as straightforward and easy by excluding.
If the game cares enough to give bad points for bad viewing or bad proximety to water treatment stations, then doesn't have wheelchari accessible ramp 'sad face points to exhibit' would be as basic and not a effort for a small group but as much as any of the other things taken into account in PZ as a representation of things zoos have to thing about and get bad ratings for ignoring. Like half the game is about planning your zoo to get the positive ratings not the negative from guests so it's not like this is outside the focus of the game.
just having there be wheelchair uses and having their 'good view of X animal' rating be calc'd based on vantage of without using stairs would do it, just as it doesnt use staff paths to do it as guests cant stand there. there's no need to be bringing sims and its whole different genre and famously corners cutting standards into it. PZ doesnt need to simulate visitors is different furniture or social settings or sims complications, just A. Can they reach exhibit, B. can they reach shop C. is the view of the elephants any good.
with that as the bar, adding in wheelchair users, and hey, prams or walkers maybe too, that get unhappy thoughts if they cant get to habitats or shops. Would add alot more to the game than zones of distress for power transformers or a new animal do. While feeding directly into the core of gameplay for the planning/building aspect of the game.
like just tldr.
add in a cant access path if stairs if wheelchair=yes the same as cant access path if staff path, so all those 'guest thought' ratings and shop sales would be with ramps only. PZ is not comparable to the sims with all the stuff that game has to account for, just add stairs into the can guest X get to Y for some of the X's.