This would have been the perfect place to set a "Cathedral Square" type patio-plaza as envisioned by 3Dementia, with heaps of deep parking underneath. It's got the space the Mutual-Shuter lot lacks, and the income, population and traffic. Part of it could be green park, but having it largely be an active plaza would take away a lot of the worries about it being static, stagnant or undesirable. It could be, in effect, a second Dundas Square, but with treed, green and garden areas. If it had programmed activity, like Dundas Square, it could be a missing activity link between Bay and Yonge. It could even fit a tiny, jewel-box musical venue in to validate the Opera Place name.
If the backs of the Yonge Street stores were reconfigured, and the rest partially framed by lowrises with retail/hospitality on the ground level and living above...it could easily work.
http://i1098.photobucket.com/albums/g371/Canadian__National/op_zps4ffc02df.jpg