I was thinking myself that something like this might be a good idea, but for a different purpose. I was thinking to myself about how very often, certain changes (cosmetic, internal, features, etc.) are proposed and rejected because they would result in an alteration of all pre-existing campaigns. Improving the cap-ship AI is one that many ask for, but such changes would unbalance existing missions. Now there are ways to get around such things, though they do take some work, but it crossed my mind that it might eventually become necessary to resign to the fact that the gain from adding in these features outweights the duty to remain backwards-compatible. When that day comes, it might be a good idea to then come up with a new branch of Open. I know its been used time and time again, and people who say this are met with cynicism, but... you could consider creating a version of FS Open that is no longer directly compatible with FS2, which would be marketed (well, since you're not actually selling this its not marketing, but that's the word that comes to mind) as FS3.
** Trivial Psychic ducks as members throw vegetables at him **
Sorry, but I know its what we all want. It would contain whatever core files that remain from FS2 and perhaps even hosted on HotU. How does this tie into the idea of a demonstration campaign do you ask? What was it again? Oh, ya... not only would this mini-campaign using the FS3 features be included, as newer builds get released it would serve as a benchtest to ensure that all new features work properly on all systems. That way, there wouldn't be the problem of some error being related to the creator of some misc. campaign that a user grabbed from somewhere else. It acts as a baseline reference for testing, while not taking up 30 missions and several hours to complete.
I know I kinda hijacked this thread, but I wanted to mention this somewhere, and the first idea kind of brought me back to it.
Later!