At least before the upgrade, House acknowledges that the NCR could defeat him. But it would leave them completely vulnerable to the Legion. After the upgrade, there's no telling anymore.
Or do I have that backwards? Did House say that he could defeat the NCR, but that would leave him vulnerable?
Actually, you have a point, I've not done the upgrade quest in a while, so Im used to them being the trooper faced ones :laugh:
An IIRC, Mr. House says it would be bad for twofold reasons, a. The war would be costly, as the Three Families and his Securitrons would win, but heavy costs. and B. The NCR would likely lick their wounds, place an embargo on the New Vegas Strip, and come back to try again later.
It's the same with the BoS, his reason for them is that he'd rather sidestep a war with them if possible. I read there was at one time an option to convince Mr. House to coexist with the BoS, but it was apparently removed during development.