Whether or not the Bypass is warranted depends heavily on your train service frequencies. If your goal for all-day service is only for 3 trains per hour west of Bramalea (as per
the current long-term plan), then clearly the Bypass would be grossly wasteful. But if you intend to have 15-minute local service to Mount Pleasant, hourly express service to Georgetown, hourly regional service to Kitchener and hourly intercity service to London and beyond, then constraining the passenger operations to a single track and platform at Brampton station is physically impossible. It therefore becomes necessary to build at least one additional track through downtown Brampton, which is quite an expensive prospect. CN also wouldn't take kindly to being fully limited to a single track, so basically the entire remaining corridor would also need to be quad-tracked like you mention. Also not cheap. And that's after the expensive project of building a flyover to bring passenger trains across freight trains, which is required even for the existing 3 tph plan. And then after all those expenses, the line still only provides a single track in each direction for passenger services, which means that all services will be restricted to roughly the same average speed, since it would not be possible for faster services to overtake the local services which themselves are only 10 or 15 minutes apart. That basically eliminates any possibility of fast intercity services.
As for when the mainline platform is being built on the north side of Georgetown station?
According to Phil Verster last year, tendering should have occurred at the end of 2019, and construction should have begun this year. But I haven't heard anything more concrete or recent than that. The
Metrolinx website lists Georgetown Station as one of their upgrade projects but provides absolutely no information on it. Not even a one-sentence description.