Likely, we'll see a few updates here and there, they'll focus on fixing some of the, well, fixable issues with patches.
Some things can't be fixed by patches (that's just the way it is).
We'll likely see a revamp in the form of an enhanced edition, they aren't the kind of company to simply run away (they put a lot of genuine work into this game, you can tell that the team was passionate about the product). I'm sure that intended content was cut, we might see some of that return in through patches.
If it's economical for them, I do hope they spend the time to give the game a once over in the form of the Enhanced Edition, like the first one received, hopefully for free for those who owned the original. The game was, generally, great, there were a few issues that I noticed, and some issues primarily in the later stages of the game, though those were far from a deal breaker.
I'd like to see a Monk Class, I do feel like that would be pretty interesting. Some stability fixes may be patched in, either way I'd like to have them in the Enhanced. New quests, and reworked quests, along with more alternative ways to do certain quests.
In general, the Reaper's Coast main-questline to find the random masters, I'd like to see it remastered such that each one offered you a unique source skill, and that source skill came with drawbacks for using it. Something like 'Bend Will', to ensnare their very soul to your will, you can force them to answer you, or assist you in actions. Say you find a merchant who you suspect is lying to you, so while speaking to him a new option pops up, spend a Source Point, enslaving him, he now is forced to answer your questions truthfully, gives you a key or whatever knowledge you need to proceed, etc. The drawback would be that using it draws you closer to the evil of the void or something, essentially using a dark power corrupts you slowly, but surely. Make it have tangible consequences, perhaps with a new boss foe at the end of the game completely based on your alignment you might change the outcome altogether. You might fight the God King himself, or not, depending on your alignment.
I doubt that they will do an expansion though, it's likely (if at all) to come in the form of an Enhanced Edition.
I'd like to see a 'permanent' slot for an active power, one per character. Say that might be permanent polymorph wings (like enemies have), Vampirism, etc. With the difficulty scaling on the assumption that you're using them.