I agree. More races than marines would be good. Different types of Human would be good too ie. Sister Of Battle, Guardsman, Inquisitor ect.

The Eldar and Tau would make great playable races, but I'm not sure how some of the "mindless" races like Tyrandis or Necrons could be anything but mobs. There is a Warhammer40k RPG called Dark Heresy, and you can only be humans. It kinda gets tiresome after awhile.

My favorite army is Chaos Space Marines, but i have the feeling that wont happen.