Quoted:
.308 Winchester? Yes...as others have said. Just only single shot. The cartridge will not fit in an ar15 magwell. However I wonder if anyone has considered an upper that would take .308 mags from the left side? Seems a cool idea where you wouldn't have to have a ar10 lower.
Did you watch that video contained in the linked page? Is that what you'd buy, if you were out for a new AR-15? A single shot? Maybe I'm crazy, but I don't think that was the intent of the OPs question.
I did watch the video, and the guy says it can be run "as fast, or faster, than a bolt action." Don't think so. And, we don't buy ARs because we're looking for bolt action-type single shot operation.
Again, I'm not speaking for the OP, don't have any idea what he's really looking for - that answer from Franklin Armory is not why you'd typically want a .308 AR.
Again, you want to run your AR like an AR, but in .308 Winchester - that upper listed above isn't going to do it. No upper, onto an AR-15 lower, is.
.30 caliber through an AR-15 is there - a few choices. .308 Win through the AR-15, running it like any other AR-15 - unpossible.