No. They don't need more condos. Condos don't to much to generate transit usage.
What Sheppard Line needs is at least one major commercial centre along the route, in addition to plenty of busy bus/streetcar/subway/LRT feeder routes. Without this the Sheppard Line and in fact any subway in Toronto will be dud.
Anyways, Sheppard Line will never become a viable route. You have to look no further than Eglinton Line for proof. That's a route with 1 substantial commercial centre, 1 minor commercial centre, 2 major connecting subway routes and at least a dozen or so high usage bus routes feeding into it. The development needed to make Eglinton viable is light years ahead of Sheppard. Yet Eglinton Line will only move a paltry 10,000 persons in the best case scenario. If you think that Sheppard Line will ever come close to matching the ridership of Eglinton Line, you're kidding yourself.