I think most of the benefit of the transitway will be for GO, especially for the York U routes. For MT, it will mostly benefit the 109, and also give Mississauga a rapid transit connection to the airport with the 107.
If you look at the huge popularity of the 110 though, it was a huge mistake that they decided not to build the section between Erin Mills and Sq One, and have those Creditview and Mavis stations. Even more a mistake if you consider how ridership has skyrocketed on 61 Mavis since then. Too bad.