I think if GO REX is to be the GTA's version of Berlin's S-Bahn, it should just be this. No peak-only or otherwise limited service. True rapid transit service only, which means frequent service all day. The lmited peak-only service GO Train service should be separate from GO REX service.
I think that the Rush Hour peak trains are an important bridge service, because there's no way that all of these electrified services can be rolled out at once. The way I see it rolling out is all of the tracks that make up the Toronto-only service would be electrified first, with current GO trains overlapping it. They would then be pushed further out until the listed terminus points are reached. Eventually, everything would be electrified, but that's a while out.
For my my map, I did not have any REX service to Georgetown because Halton Hills' ban on local transit. I think not all existing GO Train service can be REXed. Not all places or corridors currently served by GO Trains can support true rapid transit express rail service. If a place has no local transit, certainly there is no point at all for it to have rapid transit service. I also think the Barrie Line cannot support a REX level of service.
Interesting point. What would you recommend be the terminuses of the electrified lines (this is an open question to everyone btw, not specifically you, because I'm interested to see what people think about it).
I think that the Barrie line, if the connecting routes are properly configured, can support a REX level of service, albeit not one of the highest used lines.
GO "REX" (Regional Express) is a catchy name. It was form Metrolinx document. It's pretty catchy, meaningful, sensible, etc. Hopefully they come up with a similar name for "LRT" because "LRT" is just dumb and makes no sense. I used "Tramway" because it fits with subway and busway. The problem of course is that the term "streetcar" is used in Toronto instead of "tram". Maybe something like "Metrocar" or "Streetcar RT" or something.
I think branding when it comes to a new rapid transit service is key. VIVA and Züm have proved this pretty conclusively. Going with GO REX as a branding name would be a good way of differentiating from the current GO service in the minds of people who only pay passing interest to transit.
The Transit City LRT service definitely needs something like that too. Any future Toronto BRT service will need the same type of branding.