That idea (building south of The One) is not an easy prospect.
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At the lower levels, total distance between the podium of 'The One' and the U of T owned building at Charles is only ~58M
Even if 'The One' is sufficiently set back at higher levels, you still 'have to' have a 25M separation from the building to the south.
That leaves you a maximum of 33M of frontage; but I don't see an allowance being made for 0M separation to 'The One's podium level'.
That's a bit tight.
Then you have 55M of depth to the condo wall at the rear:
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From which you again need to deduct 25M separation distance.
That's 30M
All in, there's a viable floor plate there; though setbacks from Yonge, at least will eat into that as well.
But it's workable, but very little spare room, would seem to require owning pretty much everything in that contiguous frontage.
Could be worth the $$$ and hassle.