Now you want TWO elevators per station!? I think Wheeltrans is the best way to serve handicapped riders, basically because of costly cans-of-worms like this. Also, since some paratransit will always be needed anyways.
I take it you've never been stuck in a wheelchair.
I'm in agreement that some (not all) stations need to have a second elevator.
The one that needs it most is St. George, where an elevator that's out of service (happens quite often) requires someone in a wheelchair to go all the way around the YUS loop (if transferring between subway lines) or if trying to get to street level, either making a complex transfer via the 127 Davenport and 26 Dupont or going all the way back to Spadina or Bloor-Yonge and wheeling back.
There should also be a second elevator at Bloor-Yonge between the platforms, but at least there are two accessible exits (Hayden Street and via the HBC Centre). Union Station should have similar redundancy. Once most stations get elevators installed, it would be easier to make short back-tracking possible to reach a useable elevator. I'd also argue that Eglinton should get a second elevator once the Crosstown opens.
The most fustrating station (assuming the elevators are working) is Sheppard-Yonge, where to transfer from the 84 bus to the Yonge requires a long trip, via two elevators, and going around and using the unused Sheppard platform. If actually trying to get the Sheppard Subway, it requires going to Yonge platform level and going back up another elevator.
I've had to use Wheel-Trans for four months after a serious injury. It's not ideal, and it is very expensive to operate, and there's almost no option for spontaneous travel if the transit is inaccessible - and that's right now most of the central city. The subway station near work has no elevator, the hospital I had to go to - Toronto Western - is served only by streetcars. But if work and Western were both wheelchair accessible, I wouldn't have needed Wheel-Trans at all.
You are right though that even if every station gets an elevator and all the low-floor streetcars come online, some paratransit will still be needed.