The suburban sites have been chosen because that's where the bulk of bus ridership - and therefore bus usage - is focused.As medium term measures:
1) one or more bus garages need to be closer to the core. The desire has been for suburban sites that can be all one level and cheap(er). We need to understand the deadhead distance to scramble buses into the core of the City if there's a problem make this untenable. With electric buses, a 2-level or even 3-level bus garage can be realistically considered.
Electric buses will have no bearing on how the garage is constructed. There is nothing stopping the TTC from building a two or three level bus garage tomorrow, except for the biggest factor - cost. What will have a major bearing on how the garage is constructed is the piece of land - there is very little land that is zoned as industrial close to downtown. Should the TTC decide that they want to build another bus garage closer to downtown, it may be required to have some measure of vertical storage to it, much as the Lakeshore Wheel-trans garage.
But then again, why so much focus on downtown? Large sections of the subway operate outside of the downtown core. For instance, the nearest garage to this most recent shutdown is Mount Dennis, which is about 5km from the subway closure. You're not going to get drastically closer to the subway short of the Wilson garage, which is adjacent to the subway at Wilson Station.
But frankly, all of this is moot, anyways. There are not hundreds of drivers sitting around with their thumbs up their asses. There are not hundreds of buses sitting idle in garages waiting for the next emergency. Doing that costs money, and is it really wise to put huge amounts of resources into "what-if" and "maybe" scenarios? I don't know about you, but if those resources could be used to improve services on a daily basis, rather than not - well, I think that the answer is obvious.
There are way, way more locations to have trains change directions than what you've listed. I would suggest taking a look at a track map (www.transit.toronto.on.ca is a great resource for this kind of thing) to see just how many more turnback locations there are.2) Strongly consider installing more cross-overs on Line 2, the distance on Line 1 (Yonge side) is fairly close to every second station, Line 2 has large gaps, Woodbine to west of Chester; Chester to St. George, St. George to east of Keele. Adding one intermediate location to each of those gaps would do wonders, cutting down the number of buses required and walking distances.