You are probably thinking of the wrong road. The road that would need to be moved is not in any way a "main artery" for the resort. It is a back entrance to DHS, which with a little effort and motivation, can be moved quite easily.
Once that road is moved, there's really nothing that would stop them from being able to use that land. Allow me to visualize this:
Red = BLT/LMA... Lots of potential for new attractions
Blue = Back entrance from the highway into DHS parking lot
Pink = Potential expansion land for both the park and parking lot once the road is re-routed
Obviously it is looking way down the road before we see any of the pink land used, but I do think it will eventually happen.