There is a crossover at St. Clair, immediately south of the platforms. It's not tied into the signal system however, and won't be until the ATC/ATO is installed.
That said, they could use it as they did the unsignalized King crossover earlier this year.
And for the record, the reason why they don't extend the subway service to Davisville is because they are concerned with the small bus terminal located there, and having it get easily overwhelmed by the crowds using the shuttles. The trains themselves were turning in the Davisville build-up, on the third platform.
It can't be done over A weekend. It will take some time to do it, which may involve multiple weekends.
But considering that they still don't know exactly how they are going to fix the area, don't you think that it's a bit premature to state unequivocally that they will have to shut down the line for two weeks straight?
Dan
Toronto, Ont.