Definitely no sequel coming. Part of the reason I rushed the game out (if you could call a 5 year dev cycle rushed) was because I was in school getting ready for a career in games. I went straight to the industry and worked on Ratchet & Clank and Resistance. I have thought about trying the indie game scene, but that would involve a remake of DD as opposed to a sequel.
Still haven't gone that far yet. Lately I've actually been writing fiction under the pen name Domino Finn:
I've sometimes thought about making a Diver Down novel!
It's interesting to note that the fantasy world of Minduul began as a novel I never finished when I was younger, but the whole sci-fi aspect and Drek was a different storyline just for the game.
All those plotlines to explore further sound really intriguing. I planned for tons more things, like more Hunter's Guild missions, more optional arena fights, boat combat (or at least one sea monster), a lost frontier, etc.