I have considered this idea in the past, and it would certainly look satisfying on the map. But like
@Northern Light said, it is extremely unlikely that the cost could be justfied. The main reason is that Newmarket and Aurora themselves make up such a large portion of the line's ridership. If it were a line which served many intercity trains continuing onward to major cities beyond Barrie, then it might be worth having a dedicated intercity line bypassing the commuter centres. But it's not worth it just for Barrie, Collingwood and Orillia.
Unfortunately I don't have time at the moment to do any back-of-the envelope calculations to ballpark the time savings it would bring.
A much more practical improvement for Bradford, Barrie and points north would be to run limited-stops services on the line. Given that trains currently run the line in 1h40 making all station stops, express trains could easily run the line in less than 1h30. Once the line is double-tracked from Union to Aurora as planned, it will become possible to have multiple stopping patterns for the all-day service, with express trains from Barrie and local services from Aurora.