The ultimate thing would be something like an expansion the same size of D:OS2 itself, but with the acts developed in parallel so they stay the same quality.
Oh how I would love to continue the adventures of my gang.
Having said that: I'm not sure if I would like starting at level 1 or continuing at level 22 better, both options would be fun.
Qualitywise... I'd love to see more intense, thrilling Fort Joy style stuff and less Arx (or Nameless Island, which was, for me, the weakest part - because it was so "unrelatable").