I agree with Paragraphs 1 and 2 of your post.
Concerning Paragraph 3, I do not know the answer at this point, and suspect that nobody really does. The climate has changed and the need of massive transit investments is now recognized. However, the actual funds are not committed yet, and the mechanisms to raise them (I'm afraid, no way but to create / raise certain taxes) have not been tested.
Technically, we are still at about 2.9 B of committed funds (1.4 B provincial for Spadina extension, 0.7 B federal for Spadina, about 0.8 B provincial for Yonge signal improvements and a bunch of smaller projects) plus about 10 B of promised but not committed yet (MoveOntario announcement less the amounts already counted in as committed). This is not much, compared to the 25 - 26 B needed for Phase I of subway-centered plan (as my estimate above suggests).
If the needed funds can be raised, then of course it makes sense to look ahead, and build subways in the corridors that will likely need them eventually.
Otherwise, we might have to make choices. For example, extend the Sheppard subway, but settle for LRT on Eglinton. Or vice versa, build subway on Eglinton, but LRT on Sheppard, or defer the latter corridor altogether. Here I'm not suggesting either solution for those two particular corridors out of the network context. The point is that the actual Phase I plan has to be network-based and fiscally attainable.