I know what you're saying, but I think that the economics might be against us. I think it's difficult to pull off something like the St. Lawrence neighbourhood today, and not just because all levels of government have effectively pulled out of the housing game. When St. Lawrence was first developed in the late 1970s, the value of that land was practically worthless. It was the remains of a disused railway marshalling yard on the edge of a downtown that few people cared about. Today, that land would be hard to convert to affordable, family-friendly townhomes, and I think that high density apartments is the only profitable option. If you want families to live in urban areas, I think the better bet is to get governments to allow density and mixed uses and also rebuild streets for more pedestrian-friendly uses on the "urban" edge: places like South Scarborough, the Queensway, Weston and Mt Dennis, parts of East York, etc. - and build the next generation of Bay and Gable-and-commercial strip neighbourhood there.
I also think you're still romanticizing the conversion of Bay and Gables to triplexes too much. Frankly, the reason they're being converted is because we are undersupplied with apartments (i.e. non-family housing) in the core, and we are resorting to turning formerly single family housing into apartments. There are two problems with this: the first is that those 100 year old semis were never meant to house 4 units and the conversions are shoddy and structurally poor (this is especially true of basement suites in buildings where the basement was merely supposed to store firewood). Secondly, and perhaps less importantly, converting Bay and Gables to multi-unit apartments often destroys the beauty of these buildings as facades are marred by ad hoc balconies and staircases built to service all those units.
