Well Metrolinx is counting on GO can serving local commuters. As the article below says, they're working towards "growing integration between the TTC and Metrolinx, blurring the distinction between urban and suburban services". Basically there's no need for western extensions because the Georgetown line would be the DRL in the west end. Building another line on that same corridor would be wasteful duplication.
Interesting from the TTC general manager in that article. As the article puts it, he supports GO building stations and fare structures in some areas of Toronto in such as way as to provide a reasonable local commuting alternative.
"At some point the downtown relief line may need to be built, but you don’t build it until you’ve exhausted all ways of moving people in Toronto, on TTC, on GO"
They're using some very weak wording in that first quote, like the TTC still wants to fight integration and only accept it in specific places where they absolutely have to. They also seem allergic to the DRL and want to delay it as long as humanly possible. I have no idea why. Sounds like they still want to operate their own little feifdom and their position is constantly going to be an obstacle to proper transit in Toronto. Hopefully Metrolinx will completely take over mass transit expansion and the TTC will be told to stick to operation.