I'd be happy if they would expand Azeroth out to real size, not the scaled down world we have now, and allow the players to make their own towns, ala Warcraft, and then build those towns up, interacting with other towns and the wilderness... attract lumberjacks, craftsmen, etc. etc.. allow wars and political stuff.

Sigh...

Ok, see, it's just a question of time. blizz will come up with tiny lil' statements for us, the community.
Until this happenz... mwooaha^^ well... *speculating* still Starcraft could make a nize addition to the bunch of mmo's we're currently seeing in development as it would be:

-Next gen in style
-Next gen in setting
-Next gen in engine

However, "Starcraft: Worlds" could look like this:

-Multiple planets, each with unique region (think of relatively small areas of content that may expand in future addons)
-Space vehicles settings. Maybe , to travel to some parts of the universe you'll need to "survive" a certain time on a zerg-infested whatever-spaceship like a raid goal or something.
-For equipment maybe a class would have it's armor and then, unlike the typical chest-arms-head-trinket-a.s.o. system you'll be able to upgrade your stuff otherwise . Just think of armor sets in WoW?
Wellwhy not installing a couple of superhardtobreak-zerg leather on your space marine's plate mail?
Buy legendary high tech blaster weapons and so on.
-Factions: Maybe only Protoss and Humans can be played? doesn't seem like THEY need new claws to equip on zerglings, do they? xD
-Protoss equip may rise from psionic cristals (as seen before) , shards and other miscellanous things. it isn't said that both, humans and protoss need to use the same equipment syste at all.
-PvPvE could take place massively (like announced in the upcoming mmorpg AiOn-ToE).
-Maybe a part of the game takes place in open space battle? having to control a small spaceship or huge carrier? think of elements we've seen on eve online! (maybe simultanously half of a raid has to fight inside the ships agains intruding zerg or else, adding raid content to this aspect of the game)
-Next Gen healing management:' yes, we've seen the pots-only system on diablo series, and the classic healer-heals-everybody-and-does-nothing-else in WoW too, think of bandages? yes! got it! Sure, the shall be classes like Med's but why do not have them to be NPC that can be called in?
-NPC-supportetd fights. In (so far i am informed) all mmorpg we know it's only the team of players themself who hit their enemy. Think of NPC troops, called in or commanded by a PC officer, now adding great tactical features and equally allowing a "Necromancer-like" gameplay for all those who like that. (might be restricted to the "troup commander"-class).
-Every unit will have a dead zone for ranged attack like we've seen for hunters in WoW too. So melee becomes more interesting for everybody.
-Armor system may now be independant of the hero lvl but add special abilities to your armor such as regeneration or improved throwback effects..

so far from me^^ feel free to flame now^^

Well the "next gen" tag has gotten old and there is confusion on what to agree on a definition. Most of it is marketing driven and really has no basis in what I believe would be the core concept of what it really should mean.

If we all look at how MMO's execute their game play and the great majority use a very simple approach what I cal the FedEx approach. This means you get a quest go (pick up, kill, loot >insert here< ) and deliver back to the quest giver and finish the quest. This has been done since the ancient days of game play and hasn't changed that much, just variations on this concept. WoW merely polished this concept to a high sheen even if it a boring one.

My definition, in part, for the "next gen" would be a totally new concept of game play (and yes we heard that phrase too) A break from the FedEx line of thinking and that would be building a branching concept like that of a tree very much like in real life. Imagine you having alternates that will never have to repeat any of the game content that a previous alternate has done. A new AI would have to be thought up to handle that. among other things. This would be a huge undertaking in terms of time money and resources. This would be the "total immersive" world that game devs have talked about in the days of yore. Whether it'll be ever done, we can all dream.