I'm not sure what you're getting at here.
A GO platform is like, 2x the length of a TTC subway platform.
ML has indicated in the GO expansion IBC that they intend on having something like 7-10 minute frequency, excluding express services, on most lines.
On the double track lines, if we just ran 12-car single level trains every 5 minutes, that would already be basically the same capacity as Yonge or B-D subway currently.
With some signal upgrades and higher frequencies, plus double decker trains if it were really necessary, we could fairly easily 2.5x or 3x that capacity if it were needed.
On the quad tracked lines, ultimate capacity is even higher (obviously).
Well, if the demand would rise as high as you suggest, isn't that a success story? Where these are exclusive GO ROWs, can't we just add more trains and provide more service?
Seems like a good problem to have! And I imagine it would help to ameliorate concerns about Yonge overcrowding and the sufficiency of Ontario Line.
Great if so. But I see more than a few problems with that:
1. The load / unload speed. Just look at the GO car door layout, and compare to the subway car door layout. The GO cars are a lot less efficient, and the double deckers are the worst. That's not a big problem when the trains run once in 30 min or even once in 15 min. But try going to every 7 min or every 5 min, and you might not be able to pull the next train into a busy station because the previous train is still sitting there unloading.
2. Platforms at Union: do we have enough of them for all services?
3. Stairs / elevators at Union. Compare them to the subway stairs; the latter are a lot wider. Can the Union stairs handle the subway scale loads?
4. GO trains require full break tests every time they change directions. Perhaps we can organize the frequent GO lines in such a way that none terminates at Union / all run through Union, that should help. But they still need to terminate and turn back somewhere; can they do that trick while maintaining a 5-min frequency?
5. Track conflicts between services. Yonge subway tracks and Bloor subway tracks do not cross each other at grade, obviously. But today's GO trains use routes / tracks that cross each other. Again, fine for 30-min frequencies, tight for 15-min, not suitable for 5-min. Can grade separation be added at every place where needed? Not sure again.
Now when I see a Metrolinx report, vetted by the engineers and stating that yes, we are going to 20,000 - 30,000 pphpd capacities on the major lines, then I'll happily throw all the above concerns into a garbage bin. But before that, forgive me for being a little skeptical