Why don't you make a thread that consists on a kind of competition, with all missions displayed and listed, everyone grabs a mission and tries to alter it to the best possible thing (perhaps after changing the weapons and stuff), and then people vote in the end and bang, we get FS:R?
Perhaps chaotic, but would present a possibility for everyone to contribute to the campaigns that are the most central ones to everyone in here.
This might work except for the fact that FRED academy hasn't worked out too well.
FWIW, I agree with Black Wolf and Goober5000 but would love to be proven wrong. Changing some of the events so they are timed better, changing the balance issues so they work better, changing the AI, etc would all be good improvements. But changing the VA or rewriting entire missions or adding new ones? I don't see that happening without a LOT of contention, to be honest.
And I don't think you can look to ST:R as the be-all example as it doesn't necessarily fit the bill for several reasons. ST:R changed the original ST from a FS1 expansion to a bridge between the two games and their established facts, even if there were creative liberties. With FS1 and FS2, those stories don't have closed bookends like Silent Threat did.
I can see individual missions being redone ala High Noon and Bearbaiting, but given how much contention there is on the forums between small teams or when different models for consideration come up, I'm very curious to know how it would all play out.