My biggest concern is how this may affect the future USRC speedups (30/45kph approaches in the future) that was supposedly necessary to raise throughput to 49 trains per hour. The pillars needed for this park will absolutely require strong coordination with Metrolinx over this. Prefer mostly pillarless options with massive trusses, to keep future flexibility. Otherwise, you will be essentially locking-in the USRC layout.
If this can be coordinated with Metrolinx simultaneous with electrificafion with a 100% dual-mode locomotive and EMU fleet and switching to electric-only operations under the park, this could tie in really well. Applies to VIA too, give. HFR desires, with only extremely limited diesel loco ops (e.g. Canadian). Circa 2030, unless accelerated for Expo 2025?
Still need to solve the flying pig epidemic first.
Good point on VIA HFR/HSR. That will need some key consideration. Another point: CN still uses the passing tracks to the south of Union.
One thing this park will have going for it thought is that it must only support people, soil and vegetation, artwork, and any other park amenities on top. This should reduce the need for pillars and increase the feasibility of supporting it with wider trusses.