My bet is that the next game will be VF2. It was so wildly popular, that I'm certain they will make a 2nd chapter soon. On the other hand, as mentioned previously, both FT & PT are seriously overdue for a part 2.

As to how they can keep the VV series going, I would suggest starting over with VV1 but move the setting and technology forward a hundred years. Then move on to VV2 etc updating each in turn. We could wind up with VV2100 set as a futuristic colony set on the newly discovered "planet" of Isola somewhere in the Alpha Centauri sector of space.