Sure ... but that hasn't stopped them in the past, and there is no plans to close them. It didn't even stop them recently extending Danforth 2-cars into the curve - rather than on the straight-section at the other end!
If having yet another station with a bit of a curve at the end of the platform is only impediment to having a major downtown station, then it's a price worth paying.
The long-term numbers seem to show that Union station is going to remain a major bottleneck to operations in the future, with a limit on the number of train movements through the station. One way to decrease dwell times at Union is try and do things that make it so that you don't have 98% of the passengers trying to get on or off the train there. One way to do this is to build a DRL that intercepts GO lines in both the east and west (Gerrard Square? Cherry? Exhibition/Liberty? Queen/Dufferin?), and siphon off signifcant GO traffic there ... in the same manner that in Montreal, that Vendôme siphons off a lot of the traffic on trains heading to Lucien L'Allier (Windsor).
I agree with this completely. Have a station in Liberty Village in the west and in Riverdale (at Queen East) to intercept people, and provide more options besides just Union.