Plausible DLCs like new companions are unlikely.

Maybe a DLC for extended current companions is likely.
New gear for sure.
Maybe an arena mode or scenario mode to replay your favorite encounters.

But anything like Descent into Avernus I would say is far more than couple years away if ever.
I would definitely love a mini DLC like help Karlach get the engine fix she needs... that could be possible, they did tease that...

But anything beyond that I very much doubt it...