I think Blizzard can do better. Swarmhost was almost what they needed for Zerg but not quite. My big "fix" idea for SC2 is to fix the pathing to be more like BroodWar, these huge big deathballs walking around and stutter stepping up ramps when its controlled by 3 tanks is what makes the game crappy - you cannot control space. The good thing about swarmhosts is that they sort of artificially give back that feeling of space control. Making the maps more hexagonal and units move differently would fix a lot more. But, Blizzard will certainly not do that.
BW pathing and mining/worker movement would be on my LotV wishlist. But sadly I just don't see it happening.