Mr. House doesn't leave the Mojave as it is though. Like he said himself, 10 years down the line? He'll have the Mojave cleaned up with his unlimited army of securitrons. 20 years down the line? The reinvention of space travel. A few more years down the line? Space colonies. We know space colonies are a possibility, it's what the Enclave was working on before they got the shit nuked out of their home base, and that was decades before NV.
Not to mention all the technology from Big MT and the Sierra Madre that could greatly benefit House's space exploration. Those sierra madre slot machine things can basically make anything from what's inside the chips. Hell, before the bombs dropped they were working on making them for the military to make ammo and whatnot. The possibilities are endless with Mr. House and the technology found throughout the game.
The problem with the Legion is that instead of going foward, we go backwards, and not using any of this wonderful future tech seems like a complete waste to me. House would not only use it, but probably in all likelihood make it better, he's a super genius after all. Plus, imagine if he started selling his immortality machine to people? That's even more money, and with the Big MT's tons of tech he might even find a way to improve the immortality machine so it doesn't make the user look like a moldy grey potato.