I'm sure there aren't any current plans for a new Drox Operative expansion, as Soldak's new game is in development right now.
I had made a thread
* where I posted some of my ideas for an expansion and asked others to post theirs as well. You can post your ideas there or here and I'm sure if they decide to do a new Drox Expansion that our ideas will be taken into consideration.
*Interesting fact: I made my expansion idea thread literally one hour before Soldak announced the new game.