From what I had read, the ride cars will be re-decorated and re-themed as disney David mentioned and the ride track will remain the same, but also re-themed.
Having ridden it many times, I think it is very unlikely that they could make a safe wheelchair accessible ride car. There are too many things about the ride that would make it impossible to attach a wheelchair securely enough to the ride vehicle - sudden stops, swerves and the 60 mile per hour loop outside.
I am hopeful that thy could come up with some sort of accessible car that old be easier to get into. Maybe, having the side open up or something so the passenger with a disability doesn't need to be lifted over. It is a 2 person, not real easy transfer for DH and I to get DD in and out.