Amendment for OP -
Last Spring when I was at WDW, there was still a separate handicapped boarding area.
I just rode today and both regular and Fastpass lines are accessible until just before boarding. At that point, there is a pull off for guests to park their mobility device and walk to the ride car.
My guesstimate of distance is about 15-20 feet from the wheelchair parking area to boarding. You have to cross and walk on the moving walkway to get on.
The distance is similar to get off and the moving walkway ends in a bar across the path.
1) Alas, not all rides can be retrofit.
2) Peter is one of those.
Yes.
I have explained before to people why it is 'must be ambulatory'.
There is possibly for people who are not ambulatory to maybe ride the first run or the last run of the day. Check at the attraction, because other people have been able to arrange this at times.
Because of the track being suspended and in the dark, they only do emergency stops. So, when they have done this for guests who would not be able to walk on, the rest of the tide cars are empty.