You'd probably know this: how much of the underground work for the Fort York Line already exists? I was under the impression that both the Air Canada Centre's Galleria and Telus allowed provisions for it, and I was almost positive that they even built a tunnel box under Union Square while everything was hoarded up for Telus.
My first reaction to reading about the suggested closure of Bay was horror, but after thinking about it for a few minutes it makes perfect sense. Would it not be even better to take the tracks into the current GO terminal tho? Or take one set of tracks into the GO terminal, and then continue it eastward along the Esplanade and out to the Distillery.
If you look back in history, streetcars ran on Front St from Bathurst to ? (I can't remember at this time). This included parts of the Esplanade, east of Church St.
There is a tunnel under the AC with provision of a portal on the west side of it. Fort York west of Spadina was built for tracks thou City Place saw no need for one nor did they want this type of road.
TTC wants to run a Bathurst car into Union once the line is built as well the the Waterfront line.
There is no way streetcars/LRT can run into GO Terminal as per your idea, as it would have to be underground 100% and that's big bucks. You need a larger radius turn and no room to do it.
TTC is calling for 8,000 riders a peak time for Union for all the lines, but I and other are seeing 12,000 plus and this is before the full Portland is fully redevelop in the next 30 years.
The Chief city planner current and past have said "how are you going to move 100,000 riders across Front & Bay as well move them up Bay, let alone Yonge, York or the Path without reducing traffic"? Closing Bay to traffic is the only answer and does not sit well with traffic engineers. There are calls now for wider sidewalks on Bay.
You every try walking north on Bay from Front between 4-6? It's a flood coming at you to the point that you have to walk on the road.