An idea for serving the STC area after the subway is build:
1) Chose the Brimley Rd route, and place the subway terminus in the area bounded by Brimley, Progress, Borough Dr, and Triton Rd. Basically, that's just east of Brimley and north of the SRT path. A new bus terminal would be located in the same area
2) Once the subway opens, do not completely de-commission SRT. Remove the section that runs between Brimley and Kennedy Stn, and build a new station at Brimley.
Thus, we will have a short route serving 3 stops in the area: Brimley, old STC, and McCowan. Since the SRT cars will be refurbished, and the greatly shortened line will require just a fraction of today's car fleet, it shouldn't be difficult to select enough cars to operate until 2030 if needed. The old yard still can be utilized.
3) Before 2030, the city should figure out what kind of transit it wants to see in the today's East-West SRT corridor, and hopefully come up with some funding as well. At that point, SRT can be retired completely and replaced with a new service.
That new service can be a high-floor LRT that runs along Sheppard to Don Mills Stn, and then takes over the Sheppard Subway tunnel. Or, it could be a low-floor LRT that's compatible with the future Eglinton East and Finch East LRT lines.