I just flew over the weekend... at both MCO and CLT, they called for pre-boarding, Zone 0 (?), military and Diamond Elite first (all as one group), then followed by Zone 1. There was no separation for Gold, Platinum, etc. elite, we were just grouped in with the Zone 1 people. BUT, the Zone 1 line was a bit shorter because some had already boarded.

Of course, at MCO there was a small contingency of people who weren't in any of those zones who tried to board with the very first group anyway and slowed it down for everyone, but that's probably a universal problem that can't be fixed.