Well, 17 missions of BP2 R1 only took roughly a year to fred. So that'd be about two years for FS2 campaign.
BP2 was working to a single vision, Darius', but there was also room for flexiblity, in that regardless of BP1 it's all basically new and therefore you are not bound by previous canon.
I think you'll find about twice as many ways to interpret the main FS2 campaign as the number of people you enlist in any project to upgrade or improve it. Or possibly three times. Hell, I personally have gone through about five major variations.
ST was so minimalist in depth and scope that you could get away with almost anything as long as the Hades, cruiser group Hellfire, the Krios, and Jotenheim Installation got whacked. How you did it was pretty much up in the air anyways. In FS2, the way you accomplish certain Stations of the Canon will have a serious effect on how the campaign works as a narrative.
So yes, if you want to find new and interesting ways to piss people off...go ahead?