I mean in terms of track improvements. They should reconsider full double-tracking but the upgrades should be enough to get to 90 minutes. Weekend service needs to happen to Mount Pleasant now though.
The planned track configuration can support 2 trains per hour between Kitchener and Georgetown. There is no need for full double track in the current planning horizon, but that's something which can definitely be done at a later stage.
Thanks for the update on Barrie. I wish they would move the south Newmarket station, it feels like they won't do the second platform at Newmarket GO. Barrie south needs a second platform no?
Newmarket eventually needs a second platform because the plan is for every 15 minutes to Bradford (i.e. double-track to Bradford).
But in the meantime my guess is that their next step will be sidings to support 30-minute service, similiar to what they're building right now between Kitchener and Georgetown. The current peak service is every 30 minutes to Barrie so those sidings would be required before there can be any counter-peak service. In addition to the siding between Bradford and Innisfil (for hourly midday/evening service), half-hourly service would also require second platforms/tracks at Barrie South and East Gwillimbury.
30m to Bramalea should especially be doable given the low UP frequencies rn, but given the layout of the tracks on GTS right now are there actually passing loops for trains to operate every 30? You can't quite make it to Bramalea in time otherwise, and clearly the 4th platform hasn't started at Bloor and isn't done at Weston
30-minute service to Bramalea doesn't even require the existing third track, let alone the fourth track under construction. The average speed of GO's local service is similar enough to UPX that they can slot between the UPX trains on the two western tracks - even while UPX is operating every 15 minutes. The UP Express timetable already leaves gaps at Wice (Pearson Junction) to allow an eastbound train to reach the south track without conflicting with UP in either direction.
It makes sense that the current hourly off-peak GO service uses the 3rd track instead of the 2 UP tracks. If the track exists, we might as well use it to reduce the chance of interference between the services, and be able to serve Etobicoke North station. But it isn't strictly necessary. One compromise option could be to run the hourly Mount Pleasant trains on the 3rd track as per the current pattern (since they have a higher chance of delay), while the hourly Bramalea trains share the UP tracks.
But to actually answer your question: the new 4th platform at Weston will enable half-hourly single-tracked operation on the 3rd and intermittent 4th tracks. Trains would meet at Malton, Weston and Union.
I don't get why the 8:34 from Union to Mount Pleasant is cut - and replaced by a single "31X" bus that makes all stops from Malton to Mount Pleasant. That just seems weird, unless there are still not enough train crews to make that work when extending other trains to Kitchener, or if the capacity is given up for UP Express.
The 8:34 from Union used to arrive in Mount Pleasant at 9:23, then turn around and operate the 9:40 eastbound from Mount Pleasant to Union.
In the current schedule, the 9:40 eastbound from Mount Pleasant now starts in Kitchener at 8:45, so it's operated by a different trainset which is stored in Kitchener, making the 8:34 westbound unnecessary.
But given that the 9:34 westbound now continues all the way to Kitchener rather than turning back to operate the 10:40 eastbound from Mount Pleasant, that raises the question of where that 10:40 eastbound train now comes from. If it deadheads from Union, then surely it would be better to just use that train on its old schedule to Mount Pleasant, and shift the Kitchener-bound train a bit earlier. The Kitchener train can't depart along the old 8:34 schedule because it would get to Georgetown at 9:34 which is too soon after the eastbound train which departs Georgetown at 9:30. But it looks like there's room for it to depart Union around 8:55 or 9:10, operating express to Malton on the centre track, then all stops to Kitchener.