I think you would need to do the DLC as not so much an expansion but another game. Do a DLC that is just a new campaign, just the story needs to be done, the assets for the engine could stay the same. You again start at level 1 and then go through the new campaign. In this manner the game could have multiple "DLC" provided they can keep the story plots well done. Each could be stand alone and so less pressure for people to purchase any or all of them.
Tactical Adventures gave us Solasta CotM which did levels 1-12 then Lost Valley DLC which did levels 1-16 and had nothing to do with CotM then lastly Palace of Ice DLC which went from level 10-20 and was the culmination of the CotM campaign.
Maybe Larian could do a sort of "spin-off" DLC where you get to follow some sort of story based on an option you didn't take in the main game. Or some sort of tying up loose ends thing.
I feel that the real problem of CRPGs generally is the main plot. It is usually just a variation on a theme of "bad person seeks to take over or destroy the world". It's been done to death over the last 25 or so years.
Maybe "The Future of CRPGs" is the subject for another thread but there again, half the people on here don't seem to be able to move on from BG1.
