I disagree with this on pretty much every level. First of all, New Vegas factions weren't that 'grey'. I wouldn't trust the judgement of anyone who couldn't distinguish which side was the good and bad guys between the democratic NCR and the enslaving Caesar's Legion. Secondly, I'm not the least bit interested in going to war against good guys. If the Empire and rebellion don't present clear good guys and villains, then there is nobody to side with. I'm certainly not going to help one faction kill the other over what amounts to a difference of opinion.
Uh-huh, and I'm not going to derail the topic by pointing out precisely why most of the factions in NV are grey. If the main quest is some derpy "Good Rebels versus Evil Empire" garbage or vice versa I'll be avoiding it completely. I realize quite a few people are satisfied with that kind of simplistic story telling but I like my soup a bit thicker.