Also I would submit that a fan project need not take several years to complete, but that a project such as Standoff had not only to force the vision engine to do what they wanted but hack it to death to give it the feel they were going for.
A fan mod, for example, that followed another Cerberus or Midway around the galaxy wouldn't have the need to to hack everything the same way, or to create all new (and graphically beautiful!) ships and textures to fit with their designated 'theme'.
Well, you're partially right there, but my point is that we've seen neither in years - it's been 6 years since I started working on WC2-era ship models for what would eventually become Standoff... it's been about 5 years or so since I chose to go with the Vision engine (before the UE source code was out), came up with a storyline and then started getting help from the former UE guys... And nobody has really done anything with the engine since. Not another Standoff type mod, and not a "mission pack" type of thing for SO or WCP either.
Now, while you are correct that Standoff would have been done long ago if we didn't keep hacking the engine as we go along or chosen to replace basically all of the graphics, those things didn't take up the bulk of our time at all (and I'm not even counting 2006, The Year In Which We Did Nothing, either
).
Basically, what you could come up with in a relatively short time (assuming this isn't your full time job, anyway) are conventional WCP/SO type missions, with no new gimmicks, no cutscenes, nothing that might screw up debugging or require new functions, etc. You could probably come up with a UE-length campaign using all stock WCP/SO resources in a year, maybe a bit more. But again, my point is that even so, we haven't seen this.
And of course, even if you did that, you would then, inevitably, want to add something else to it.
Voiceovers, in-engine cutscenes, new comm videos, perhaps fiction, a new splash screen, or even talking head cutscenes like Standoff's. That's where you're screwed. Heck, by adding voiceovers alone, you've already managed to secure yourself one Behemoth-sized headache (if I hadn't handed this job over to Tempest, we'd be taking even longer to finish this thing. I'm not sure how he does it.), and it's probably something that most people would consider a necessity for any good fan project nowadays.
It's not that these things are intrinsecally tough to do, but it just starts requiring more talent in your team, and adds whole new levels of complexity that are almost guaranteed to screw up your project coordination and add a whole new range of things that can go wrong. It only takes one voiceover actor disappearing five years into the project but one month before the final release to completely screw you over.
(On a side note, the only reason we even have such an absurd amount of ships is that I usually got bored and decided to do *something* while other parts of the project that were more work-demanding or prone to delays and uncertainties were still lagging behind... So we have lots of ships and new cockpits and menus and et cetera because we took too long to finish the game - not the other way around.
)