I don't think so. The entire raison d'etre of the Sheppard Subway was to connect STC to NYCC, which were presumed to have well developed "downtown" cores by now. Unfortunately that development never materialized, as office development trends across the GTHA shifted towards Downtown Toronto. This left the Sheppard Line without much of a purpose to serve.
Today, any Sheppard extension would primarily serve to bring people from Scarbrough and North York into the Downtown core. However this extension would not be particularly effective achieving that. The route from Scarborough to Downtown via the Sheppard Line and Yonge Line would both be very slow, and very overcapacity (it would be practically useless during rush hour). People would be calling for a faster and less crowded route downtown.
With hindsight, the Sheppard Subway proposal should've been scrapped, in exchange for a subway route running along Don Mills or Victoria Park to the Downtown core. It would have been much faster at getting people Downtown than the Sheppard Subway proposal, without any of the Yonge Line crowding issues. A BRT would've been more appropriate for linking STC and NYCC.