Well the main thing to consider is that it's not possible to restrict a passenger's movement around the bus. A wheelchair user would be treated just the same as a normal passenger, i.e. they'd go upstairs on a double decker and sit inside existing seats. While you theoretically could make a wheelchair user, the game isn't designed with them in mind so it wouldn't work too well.
The best solution I could propose would be a little similar to the Chicago bikes - nobody is carrying a bike when they are at the stop, nor do they walk off with one when they leave, but a bike is on the front of the bus while they are. Equally nobody would board or disembark in a wheelchair, but one would magically appear beneath them when they sit in the wheelchair bay seat.
Oh, I've never doubted bicycles were possible, it's just that you have to model a person and a bicycle to be able to do it. Indeed with OMSI 2's AI groups system, it's better than ever because you can mark particular paths for them to use.
I'm very sceptical of LOTUS at the moment. It's looking (from what I've seen so far) like the graphical fidelity hasn't really improved and that the singular developer is going on too broad a spectrum (I mean planes? Come on m8, this ain't FSX). I guess I'll just have to wait and see. But in any case this comment has been wildly off topic, so I'll just quickly say that wheelchair inclusion is a cool concept it just doesn't seem possible atm.