This is a good point. I'd expect them to do exactly what they did with the Yonge North Subway Extension back in 2007: Commit to studying the project and perhaps progressing it to an EA. They are unlikely to commit any dollars to the Sheppard Extension, but that won't matter anyways, since voters won't distinguish between committing to work on a project, and committing funds to that project. The Liberals will also point out that the PC's transit proposals are not feasible with the funds they want to commit.
They'll commit to building the Relief Line Short, and further study of Relief Line Long (the latter of which is not news). The combination of DRL Long + SSE will likely be a winner for them in Scarborough.