Well, there's a bit of a difference between places like Liberty Village and places like Jane and Langstaff (which is on the way to Major Mac). While it wasn't obvious that these places would become the hot places they were, the seeds were sort of in place: a place like Liberty Village has old historic industrial buildings of multiple stories that are still built on a walkable grid. The properties are relatively easy to convert to other uses. Moreover, Liberty Village is located close to a downtown that has seen incredible revitalization over the past 20 years. Looking ahead, it's not implausible that similarly industrial areas like, say, the Studio District will look more like Liberty Village in the future, or that the industrial areas near Eglinton and Laird will be upzoned to take advantage of the new EC-LRT, plus the historic desirability of nearby Leaside.
This is a bit of a different story from a cement silo or logistics warehouse in a 905 industrial park. For starters, these aren't properties that are easily convertible or desirable for uses other than the one it was built for. Second, they're not next to areas that are becoming rapidly desirable. Third - and probably most importantly - there are established industrial users in the area who have a vested interest in keeping things that way. CN is not going to suddenly abandon its giant marshalling yard because some condo developers give it a good offer. This is not something that is easily replaceable for CN, and represents an enormous sunk cost. This is the same reason why Downsview remains an active Bombardier assembly plant, despite the fact that it is now well within the city, beside a subway line and across the highway from one of the most upscale malls in the region.
Back to the Midland and Ellesmere example, not only are there 2 rapid transit stations nearby, but nobody would have guessed that the low density industrial uses would outlive the rapid transit line. Yet here we are, and that's a distinct possibility.
