Just to confuse things with specifics....it looks like this weekend's work window will commission the second track from Parkdale to Nickle. That gives two tracks as far west as Nickle, and from Wice west to Halwest. Intermediate signals appear to have been turned on this far, for these tracks. I don't know if the current track alignment from Parkdale eastwards is the final one for these two tracks, however. The rest of the second track, and the third track, is clearly getting close to completion, and likely all the larger track shifts are finished. Personally, I would not bet on April 1... but I would bet on June 1.
Once that is done, the biggest constraint to added GO service is the single-island station platform at Etobicoke North. Both eastward and westward trains will have to use the same track at this location, IF (I'm presuming nothing) this station will get the same service level as the rest. I'm still from Missouri on whether it will be possible to interleave GO and UPX reliably enough for GO to encroach on the two tracks UPX will require. (But I'm happy to be proved wrong). Worst case - GO will have two tracks from Bramalea to Wice, and one track from Wice to Strachan. That's enough for a meaningful two-way service, but maybe not hourly on the hour.
As noted, getting UPX launched and running reliably will be enough of a challenge for the first month or two. I can live with GO resting on its oars for that time. It will certainly be nauseating watching the politicians and Metrolinx waxing poetic about the whole thing, likely ahead of the actual new schedule taking effect.
- Paul