Derelict would have been a fine expansion pack to FS2, it's on par with any of the original campaigns, Sync (if not for the Knossos in the Nebula plothole), Homesick and Transcend also. Despite that, I wouldn't say they would be worth of being FS3, they're not large enough in scope and use almost exclusively ships from the first two games. The only ones, to my knowledge at least, that even approach that level of ambition are Blue Planet and Inferno, and while they're decent campaigns, I don't see them as being on the same level as the ones I mentioned before.