Okay, so I was thinking about it, and while we all have forty bajillion ideas on what we would have done with Starcraft, what's done is done. So, let's hear predictions: where is Starcraft going to go from here?
I predict that once LotV is out, Blizz will pretty much ignore Starcraft for another ten or more years. Fan demand, now diminished, will not insist on a sequel. The franchise will only be picked up again if someone in Blizz wants to make a personal project out of it, or if technology makes a sudden leap again that results in new gameplay opportunities.
What startled me about Heroes of the Storm's unit quotes was how many of them sounded self-aware about the flaws of SC2, so if I'm wrong, probably what will happen to Starcraft is something goofy.