I'd rather see two structures, just to make the redevelopment less monotonous. I'd also hope that the terminal building itself is given a meaningful preservation. Not just a facadectomy, but a real preservation/conversion. I'm not sure what the space would be good for (a restaurant? spa? really ostentatious lobby?).
It would be great if those two blocks of Dundas storefronts could also be cleaned up at the same time. Again, some of those buildings are gems that I'd hate to lose (the buildings on the NW corner of Bay/Dundas and the NE corner of Dundas/Elizabeth come to mind), and most of the storefronts are pretty disposable, tho a couple I would rather see moved to the Edward side of a new development (we could have a mini ersatz historical facade district along Edward, with the relocated storefronts lined up beside the preserved coach terminal).
I'm not sure what sort of height the city will allow back there because of the NPS view corridor thing that they're worried about, but I'd like to see something at least as tall as Atrium on Bay, if not taller. And then I'd like it to be something that continues the Yonge/Dundas vibe. It doesn't necessarily have to be all covered in LEDs (the Ryerson Business Building does an okay job of continuing the stretch, and it's pretty mundane), but it should have either mixed uses, or an entertainment component, or have an interesting design.