I am huge fan of DS9, the best thing that could have happened after TNG, but I can't imagine the DS9 storyline being a good basis to make a MMOG. Basically there isn't much open ended which could be explored.
So it would have to be something totally new, that's a huge risk. I will give it a try though.
Still I would rather see a FPS/Adventure like game like the Voyager series, which I think we're pretty good and polished for that time. But then I guess it would turn out to be a console port, so the corridors of DS9 would now suddenly have lot's of obstacles to crouch behind
My biggest complaint however is that the current franchise is lacking direction, alternate time lines/realities, pff. Just get some excellent quality writers and actors (preferably stage actors) which have a passion for Star Trek and a new series will breathe the life back in the franchise.