I for one wish such a thing could be. But when we start talking about swapping different uppers I think we are defeating the purpose of the idea. One man and his rifle...like Hawkeye in the Last of the Mohicans. The AR-15 could fit that role in today's world where seldom would (or even could) a man live by his rifle...a world where "his one and only" rifle needed to suffice for protection, recreation, and let's say pest control (let's face it, even if you don't hunt per se, sometime you need to shoot a critter or two). For that and AR-15 would suffice.
However, in today's political climate (and political climates likely to come our way), I think putting all of one's eggs in that basket unwise. I am not the typical member here who thinks the current administration is the worst possible RKBA scenario. I believe far from it. However, what we've got coming at us in 2016...that's the real McCoy. Folks are going to wish they had the current occupant of 1600 Penn back here I think...in the gun control context anyway.
So for that reason, I would not want to count on an AR-15 for my only rifle. And I don't.