Currently the focus is on getting the game finished.
After release, that may be one of the possibilities that will be considered (perhaps dependent on what is decided in terms of other platforms or localizations, etc). Unless there is a specific need or great idea for something to add to the story to justify a proper expansion, more mod / GM mode support or starting on another project may make more sense than DLC.
DLC is quite a loss term it can be anything from More gear to more skills etc. Do not have to be story related so long it adds to the game.
I think it's a waste to the game not to make some DLC for it. I like DOS2 and think it would be very successful and what I think it is good mostly is.
More mod and GM support means more skills and gear and stuff for free. Mostly not going to be quite Larian-level, professional quality, but there should be some decent stuff (hopefully even better than my bard mod

I wrote up a whole thing about a Larian-supported paid mod system could possibly work, but ultimately I think it's too controversial and too difficult to pull off correctly. A properly curated paid mod system could lead to some professional level-mods. For example, I could pay people to make me custom spell effects, new models, animations, for my skills. There would have to be a very detailed set of criteria for what could become a paid mod (probably no shoe mods, hehe).
But again, it's all too likely this system would leave a lot of people unhappy. Free mods devalued, modders in competition rather than cooperation, all the woes of capitalism. I think a system of paid user content could be possible, but the game and whole company really would have to be designed entirely for it.