There is indeed space at Utopia Junction for that connector track, because there is the abandoned rail ROW of the former North Simcoe Railway (the
Northern Railway branch line between Barrie and Penetanguishene):
Red line is CPR
Amber line is the active portion of Barrie-Collingwood Railway
Green line would be new tracks on existing abandoned ROW
View attachment 172954
Providing this connector would save quite a lot of time for the northbound trip out of Toronto as it would avoid the need to do the three-point-turn to go from northbound Newmarket Sub to easbound York Sub at Snider Diamond.
That said, one advantage of the current routing is that both directions of the service pass by Langstaff / Richmond Hill Centre station, which has the potential to become a convenient suburban GTA access point for the train. And there is space to extend the platform north, in fact doing so brings the train closer to the overpass to the RHC bus terminal.