Overall, I'm not too excited about the new OL plan; there are numerous concern.
1. First and foremost, the capacity. Not sure it is worth spending money on a very costly line into downtown if its capacity limit is less than 30k per hour per direction. And yet, the proposed tight turns would make it difficult to reach 30k, and tempting to cheapen out.
2. There was a notion of reducing the cost by running elevated wherever possible. But now, it appears that the line needs to swing quite a bit south from Queen in order to join the rail corridor and emerge. That extra length will offset the cost saving from going elevated. It is conceivable that they could just shorten the western leg (Spadina instead of Exhibition), and build the all-underground line with no tight curves, all the way to Eglinton, for the same amount of money.
3. Some already pointed out: if the line has to swing south at both ends, is Queen still the best choice for the central section? Or, should the whole line be shifted south?
4. If OL runs in the eastern rail corridor, that space won't be available for the future RER expansion. That corridor isn't known for being particularly wide.
5. Elevated through the Thorncliffe and Flemmington neighborhoods: some of the locals will complain. That issue can be resolved if the elevated rail is decorated well, but the temptation to cheapen out might win instead.
6. And finally, the MSF location that will be difficult to connect to the actual line.