Nah, I've seen you grumpy, PE, this is not that.
I'm not a huge fan of added fantasy drawings for the simple reason that there's not an unlimited pile of money, and there are other priorities in the queue with varying degrees of real traction that all but preclude this getting serious attention, even at a planning level in the next decade.
That said, I would consider the use of the CPKC corridor from the Junction eastwards to be mostly straight forward and viable, because the majority can accommodate 2 dedicated tracks for GO.
There would be some seriously expensive bridges, and some retaining walls, but its not that pie-in-the-sky, because CPKC can retain in its existing capacity, and even add over-night capacity assuming GO would not run a midtown line 24/7.
West of the Junction, room can also be found for additional GO Tracks, however, if you continue to run a distinct GO Milton service to Union, that's a lot more traffic to manage, and it limits the potential service profile of any 'crosstown' type service from that point west.
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Toronto Yard has lots of spare room, 72 tracks have been removed; but ensuring no conflicting movements would likely require some costly re-arranging.
View attachment 523690
The outlined portion of Toronto yard is all former (removed) track, about 75 acres worth.