The big issue with expansion material would be additional skillsets (rather then just further levels)
For example adding in Bard and Trapmaster as a DLC pack
Since not only would they have to add those skillbooks (which is actually relatively easy)... But they would have to put in the specific drops.
THAT and they have the issue of "If everyone doesn't own that DLC how do?" especially with a GM mode.
So the only reasonable thing they could do I guess is made an entirely new area or chapter of the game as DLC/expansion
And just add the new materials as free DLC.
