At Polynesian and Grand Floridian the stations are over the main entrances and accessed from the second floors; there are elevators available.
At the Contemporary the station is on the 5th floor. There is one elevator that goes from the 4th floor to the platform.
The elevator at the Epcot station is on the departure side. Normally the people there will ask if you want to get out on that side, or get out on the normal exit side and use the ramp.
MK and TTC are ramps only, and fairly steep. Due to the way the stations are laid out, retrofitting would be extremely difficult.