It would just be a game for a different audience, casual vs. pro-gamer. Now casual sounds nasty and makes you think of candy crush - god forbid... I mean somebody who plays as a hobby, sometimes in the evening, but doesn't train for the game. For one, I can't put in the hours required anymore with a full-time job and a family. For another, the way we used to play RTSs (~2000) on small LANs was very different. Still competitive, but somehow more relaxed. Exactly this "managing your attention" aspect was missing, so the early game was more like a building strategy game, and the late game was less paper-scissor-stone and more about outwitting your enemy.

I think SC2 is fine as it is, for what it is. I would not want to take that away from anybody in a potential version 3; but I think there is space for a more casual game in the StarCraft universe, thus "SC2.5".