They need to take drastic measures to make SC2 a better eSports game in LOTV. Current eSport enthusiests want more. They want to watch the professional games in client. They want the ability to dis-connect/re-connect to a game. They want a better in-game viewership experience. SC2 lacks all of this. If you are simply a fan of watching SC2 you literally have zero reason to even own the client. If you ask me they need to make it so your main base still has 8 patches but make every other expansion only 6 w/ 1 gas. Re-work almost every unit so all-ins aren't too powerful against FE with this set up and tweak costs. Consider removing MSC from the game since it makes early game PvX completely boring to watch. Add in more "cool" stuff -- such as in the patch where Roaches move at light speed while burrowed. The engine and the game are still amazing but it is getting really, really old watching this game where almost every game is 3 base 200 vs 200.
None of this shit will happen with Dustin Browder and David Kim at the helm. The mechanics and features of StarCraft 2 are already too established in their minds, they won't change the game for the better. All they will do is rework a couple units they feel are underused, underpowerd, or uninteresting. Then they might add a couple more units. They will never make sweeping changes like 6m1g. They won't balance the game around it either.
Defender's advantage while strong in some regards really is nothing compared to Brood War. If they could rework the resource management game and force you to take more bases while increasing the defender's advantage then maybe it wouldn't be so easy to turtle and max out. You'd actually have to take like 4-5 bases at once, fully saturate them, and one big fight wouldn't be a high chance to end a game. In Brood War you have lots of units like Siege Tanks, Lurkers, Defilers, Reavers, and Templar which when positioned correctly, particularly when on defense, are capable of holding off innumerable odds. You also have high ground advantage and units that don't behave so well that you can just rush up a ramp and camp production structures.
As far as current balance goes, Mothership Core and Widow Mines should lose anti-air attacks, imo. The point of HotS was to increase the strength of harassment (which is air based 9/10 times), while these units are so effective at not only shutting it down, but make it a huge risk to even attempt. Mothership Core was put into help Protoss against certain all-ins like 2 rax proxy, etc and also making FE in PvP viable. Instead they made it way too easy to turtle and defend harassment. They should have made defending attacks in those situations possible, but not so overkill when it comes to shutting down harass. I think buffing the Infestor or reworking the Viper a bit would also be beneficial, since ZvT is all about breaking Terran's back with Muta/Ling/Bane before Terran can get a Planetary 4th base and 3/3 upgrades. Zerg needs units other than Muta/Ling/Bane to transition into Tier 3 safely, imo. The state of PvT is completely attrocious. Possible mech openings/transitions being viable to deal with late game Protoss might be nice. Tempest based armies are great against Mech, though, if you can get it up and running.