on a personal note, I would somehow like to see the shift move away from a solar system focus to a intersolar focus with the single solar system being more the equivalent of a city with surrounding tiles in civ games. that is, one, maybe two colonisable planets in a system, a bunch of stuff for mining operations, thats mostly it. think of freespace a bit, that game just "felt" awesome.
to borrow more from said game, entrance into systems could be via jump points, different ones depending on the point of origin. as you may have guessed this dosnt work all too well with the phase line concept. now, to counter the inevitable fear of wack-a-mole, ships have jump ranges limited by antimatter. think of it like the resource cost in hw, just that the way antimatter is gained differs. what you could do is automatic regneration. that would mean that you could jump a certain distance, but then you would have to wait to recover AND you couldnt even go back. voilá, perfect target. if that is the same resource you need for special abilites, then it means you have to get fairly close to your target, then wait for to get a reaonable amount of "battle energy" and then jump. couple that with a decent defensive sensor range and the defending player should have some time to organise defenses. and of course, the attacker needs to same some energy to return or risk getting totally wiped out.
of course you could add a ton of little items, like ships that improve regeneration, or places where regeneration is faster, mass objects like planets, moons, komets, whatever. those might lead to fairly interesting approach vectors/ strategies.
so ... what this "feel" comes down to is: this solar system you have would have these one or two planets for taxes, part of research and ship building, then a bunch of asteroids which now are in planet orbits but could be more spaced around as asteroid belts, komets and the like. but it would feel more open not like the unusual concentration of noteworthy objects we have now.
it may be a stupid or meaningless wish, but I would appreciate it because it would give the vaste reaches of space some meaning which are now more like irrelevant background. thats what how hw created the sense of vastness and emptiness in space I believe. and I liked that.
else, the usual stuff part of which hopefully makes it into the expansion
more diplomacy
more victory conditions
more story
campaign (if you think a campaign is not important. I played starcraft 80% at least for the campaign, screw you battlenet)