Unless they simply are not happy with what they've got

I really can't think of a reason for them to announce a DL Star Wars land and not a WDW one, especially considering that WDW's was supposed to come first. It's clear that DHS is going through a big overhaul. On the other hand, nothing evident is going on at DL or DCA nor is expected to in the foreseeable future (They wouldn't mess with Toontown or whatever they plan to replace during the 60th anniversary of the park).
Now, we don't know for sure whether this Pixar expansion is real or not, but assuming that something important is brewing at
Pixar Place, I think it would make sense for them to announce that first and then wait for the 50th to come closer and make the big announcement. Especially if the board is not happy with the addition that is going to sustain DHS numbers for at least a decade.