In regards to capacity, part of the issue is that the EA and Metrolinx report are getting further and further in the rearview mirror. Had the darned thing gotten approved/funded in 2009-10, we'd be in the final years of construction and the opening-day capacity constraints for 2020 disappear in the face of a 2030 opening day. In the meantime, the situation has worsened both on Yonge North and at Yonge-Bloor; no substantial progress on either.
So, I acknowledge that the longer we wait, the more my "shouldn't be a problem to build Yonge first," argument gets undermined. A paradox.
In theory, these ideas are fine (and in a perfect world, there would be a way to double-track Yonge and have a parallel express line) but I can't imagine any of these going through. Avenue Road and Bayview, in particular, are lined with fancy shmancy homes and it's hard to imagine the local pols ever OKing subways that would necessitate intensification. Try to imagine a Leaside Subway, even if it otherwise makes sense to have a train running under Bayview, interfacing with the Crosstown and Sheppard subway. (Bayview also has no development possible near Bloor, Lawrence and Steeles, for starters.)
Avenue, of course, ends at 401 so you'd have to cross the valley and join Yonge at Sheppard or (on my personal fantasy map) extend the Sheppard line over to the Spadina line and have the Avenue line end at Bat/Sheppard.
Bathurst might be relatively easy, in that context - already lots of apartments etc. - but you're still talking 3 or 4 decades away for any of these plans.
It's depressing enough that in the short term we have a subway extension with a complete EA that's already almost 10 years old, where almost nothing is happening/can happen and that it's contingent on another line that's 10 years away. What clustercuss of a situation we've put ourselves in.