WC Saga's campaign is theirs to choose. Since they are heading WC4 way, so, in fact, you will get your wish, when it comes to that.
But, you forget the GREATEST advantage of the Freespace 2+ engine...
FRED, the ability for you or me (should enough work be done) to produce a campaign that is BETTER than origins.
Not to mention the fact that with all the exciting work going on at the Source Code Project at the moment, it seems that it will be VISUALLY stimulating too.
What I am getting at is... Give us the ships (preferably WC1-2) and we will give you campaing, or campaigns, as the case may be.
My timeline for WC:Battleground serpent would be as follows... Good campaign 8-9 missions long, and then on, more ships, best of it would be ALL ships from WC on the project. From that point on, a lot of things can and will happen.