I want something related to the Enclave or the remnants. They could be major or minor like the Brotherhood of Steel in the Mojave. Since no one knows what happen to Navarro I think that either the Enclave remained there or set up camp in the Mojave. And having some tie into the main quest perhaps? And have the Enclave take control; if you're like me and dislike the NCR, Caeser's Legion, the Followers of the Apocalypse, and Mr. House.
It would be fun to have some sort of Enclave remnant left and "pacify" the denizens of the Mojave Wasteland....
Actually, it's mentioned ingame that the NCR took Navarro. I'm pretty sure you find this out by talking to the Remnant vertibird pilot. Plus, that's pretty much the only way for the NCR to get Bear Force One, after all.
I've been thinking about a full on Enclave remnants faction, but we're talking about a huge amount of work here and I doubt I'd ever actually be able to do it without a really good modding team. I mean, at a minimum, you'd need a new Enclave bunker. Then you'd need a skilled writer to make sure they fit into the rest of New Vegas seamlessly; can't have moustache-twirling villains in NV, nor shiny white knights in power armor. Then you'd have to have a questline where you build their power in the wasteland; if you want them to provide a viable alternative to the big four, it'd have to be a long and involved questline. You'd have to explain where they came from, and why they didn't head East with Autumn.
And you'd have to integrate them with Gannon's companion quest in some way, because otherwise you have the immersion-breaking inability to tell him that there's an entire faction of Enclave remnants biding their time in one of many hidden bunkers.
There's a reason that big quest mods are a rarity; it's because they take a lot of work to make one.