Splash Mountain's Fastpass and regular lines are wheelchair accessible until the point where guests come to a set of stairs. At that point there is a gate with a wheelchair symbol that leads to a path that goes to the handicapped boarding area at the exit.
So, you would wait in the wheelchair in the regular line (or in the Fastpass line if you have Fastpass). Wheelchair users who have more than mobility issues and are
DAS users would return to the Fastpass line.
We did not ride
Space Mountain, but some wheelchair users who have posted they went to the attraction and were given a wheelchair return time - basically, a hand written Fastpass to come back to the Fastpass line at a time roughly equal to the present standby wait time.
The
Safari at AK has not changed. Both the Fastpass and regular lines are accessible to a point just after the stroller drop off point. So, again, you would wait in the regular line unless you have Fastpass.
The handicapped boarding area has not changed and I don't see it changing because the 'regular' boarding area has no way to get wheelchairs from there to the unload area, which is in a totally different area. The handicapped tram picks up and drops back off at the same handicapped area, so wheelchairs are at the same place you left them when you return.
If you think you can walk from the stroller parking area to the regular boarding area and from the unload area back to the stroller area, you could park your wheelchair there. It is a pretty long distance though.
I am not aware of any of those attractions ever having had single rider lines, so I can't answer how that would be handled
