Well ye, GO is a much smaller and less used network, however overtime with new stations and upgrades it can definitely be like Crossrail or RER.RER and Crossrail provide much more service within the city than GO currently does, and their function partly overlaps with the function of local metro lines.
Anyway, there is no hard rule that regional services must use big trains and local services must use small trains. Either service should be sized for the future demand within a reasonable period.
Well then why don't you explain why its needed, and I mean needed and not "a nice to have".Obviously, every subsequent pair of tracks will bring less incremental benefit then the previous pair. I don't see much need for the 7th and 8th track, and they wouldn't fit in the rest of corridor anyway. That doesn't prove the 5th and 6th tracks are not needed.
That requires building the stations from the start in a very large and possible space inefficient way that would allow for many configurations to be run, especially since you're accounting for non standard track setups."how a 5th/6th track will help with the 2nd point at all": for example if the VIA platforms are on the south side and the GO platforms are on the north side, then with 6 tracks in total, you can use the 2-nd (counting from the north) for GO Express westbound, 3-rd for GO Express eastbound, 4-th for VIA westbound, 5-th for VIA eastbound. VIA trains never cross paths with GO Express. If you only have 4 tracks and the 2 central tracks are used for both GO Express and VIA, then the westbound VIA has to cross paths with the eastbound GO Express just east of Union.
We're assuming here a tunnel under the LSE corridor, which would put the portal around, here?It will be difficult to build a tunnel for the Don Yard shortcut, the line to the Don Yard (same as Bala Sub / RH GO) runs on the west bank of Don and the tunnel portal will be vulnerable to flooding. It should be noted that both OL portals are located quite a bit further from the river; at least they got that part right.
I can't speak for certain but I don't recall this part of the line being considered that flood prone, not to mention this entire area is being redeveloped already so I believe flood mitigation is already being built.