Nothing is listed yet..........but the TTC is aware of an opportunity. (I mean general, not a specific proposal).
Josh Matlow is strongly pushing for park space on a deck over the tracks north of the yard.
The Yard itself is a bit more challenging for a variety of reasons (the TTC needs the capacity and the yard would have to remain operational not only at completion, but during construction; at the south end, the footprint of existing buildings is extremely close to the yard tracks as is (separation distance); also in addition to the obvious, Yellow Creek runs directly under the subway yard in a very large tunnel.
All that said, I expect you will see development here, but not in the near term.
Also the TTC is set to transfer their HQ to the City (likely CreateTO) which will put in the queue for redevelopment; once the TTC finds new digs.