Yonge Street is lined with hirise nodes and proposals for more.
There's an entirely new Civic Centre being built at Kipling, significant new/proposed density near High Park and at Dundas West, Mirvish Village at Bathurst, and substantial density proposed at Pape and extant and more coming at Main and points east.
Lets also point out........those main roads are now mostly six-storey or more, as-of-right, and the adjacent SFH areas are now mostly 4s as-of-right, with multiplex permissions.
I'll grant those last moves are fairly recent, but they are done.
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I'd make another point, Line 1 and Line 2 are both close to capacity at key points, hence the 1.5B expansion of Bloor-Yonge, another similar project at St. George that will follow, expansion of Spadina Station also set to get underway, and then there's the Ontario Line.
I think its a bit off to imagine that we can stack another 100,000 people on or adjacent to Line 2 (or Line 1) at most points and not run into capacity constraints that will cost $$$ to alleviate.