Haha...the junket might not work since I doubt they'd venture so far from the hotel to wind up on regional rail out in the suburbs. After all, they would assume that they'd have to wait until the next morning for a train back in to the city! "They come every 20 minutes...? Wah??? But...it's not a subway..."
And I can see the politicians arguing! The suburbanites would all say "Why would we add trains after 9am when the parking lots are already full??" or perhaps "To hell with diverting GO, just turn the whole thing into a subway out to Milton!" To which the downtown Toronto types would reply "If it's not streetcar, I don't want it anywhere near my city!"
Seriously, though, I think that if they're going to make the investment into a triple-tracking of the whole route, they'll be introducing at least Lakeshore-level service.
Ahh, the Diversion. It would just be the best transit project ever. They'd have to electrify, though, which is suddenly seeming much more conceivable. they could even combine the Hurontario segment with an LRT tunnel. Unfortunately, the politicians will all say "Duh, why do we need to divert the GO train when people can just transfer to the streetcar?" completely missing the point of a central transfer point. It's like the geniuses who think that the best way to connect Scarborough Centre to North York Centre, by far the major hubs in their communities, is by going east with an RT extension all the way to Sheppard and Markham road, the middle of nowhere by any measure, and then back west again on a Sheppard streetcar.
I really think that we won't have proper regional rail, though, until GO manages to buy the corridors from the railways. That's why the prospect is probably greater on Stouffville or even Bradford than it is on Milton or Georgetown.
I love the idea of combining the diversion with the use of the Orangeville-Brampton railway. It runs right past the Meadowvale business park. If people were willing to walk a little, much of the area could be perfectly served. Alternatively, they could have a shuttle. You could even run routes (with a little trackwork) like Kitchener-Brampton-Meadowvale-Square One, which could be very popular.