without the whole system having local + express (4 tracks) then none of it ever will. there really is no point. not unless they want to run express trains from langley - surrey, then turn them into local trains for the rest of the trip.
not sure if the timing could be made to work, but who knows.
personally, i think local + express tracks would have been a good idea in the original system. but they probably didn't need it since headway's on SkyTrain are a lot more than normal subways so that can compensate to a point.
i still think they should be building the whole system with 100m platforms though... shame they re only doing 82.5m for the Broadway Subway.