It's already been proven that regional rail from the STC/anywhere along the GO corridor in Scarborough would have little to no time savings when compared to the subway without express service for the vast majority of people because frequencies at the GO stations will, at best, be 1/3 that of the LRT/subway, the accelerations will decrease, the transfers at GO stations will not be seamless, and the Union station transfer will be a huge clusterduck. It really only helps people commuting to King and anywhere south of king, otherwise, it's faster to take the subway/LRT.