Why not? All routes deserve to be covered. If not all three at once, then Heaven's Feel has priority.
It's not that I would begrudge Sakura getting the limelight for once, but I feel that Heaven's Feel as a follow-up to the rather Saber-centric Fate/Zero doesn't quite fit. (read: the Saber fanboy doesn't want his favorite girl to be ignored, corrupted by the Grail and then have a pathetic death at the hands of Shirou, her dreams unfulfilled and her heart not at ease =P)
Well, the line from the trailer was "What has come before and what is yet to come", which is peaking my curiosity. It would be interesting if they turned this into something like Amagami SS where the series gets reset every time a route is cleared, thus turning this incarnation of Fate/stay night into a 50+ episode opus of all three routes getting animated one after the other. I would at least hope so, given the clusterfuck that was Studio DEEN's attempt to somewhat combine the three routes into one story.