I don't think there is enough info to truly say how it is going to play. Just to give a play by play on the GCDs and what the job gauge does:

First, lets establish the new gauge, 3 icons, assuming to represent Opo-opo, Raptor and Coeurl, each with 3 empty pips of 1, 2 and 3 respectively.

After the Thunder clap, we use Dragon Kick, which fills up the Opo-opo gauge [1,0,0], then Twin Snakes which fills up 2 Raptor [1,2,3], then Demolish to fill up 3 Coeurl [1,2,3].

Perfect Balance is used, starting with an upgraded Opo-Opo [0,2,3], Dragon Kick [1,2,3], Opo-Opo upgrade [0,2,3] into what I can assume is an Elixir Field upgrade.

Next Perfect Balance, starts off with an upgraded Opo-Opo (bear in mind, the Opo-Opo pip was empty before this), upgraded Raptor [0,1,3], upgraded Coeurl [0,1,2], then Phantom Rush. Nothing else after this point changes these pips.

I think the most interesting point is the weirdness of the Opo-Opo pip. Your first instinct is that, in order to get an upgrade to your stance attack, you need a pip, however, at the start of the second Perfect Balance, the attack was still upgraded, despite no pip being lit up. The only change here is Brotherhood, but if that automatically upgrades your actions, why is it the Raptor and Coeurl lose a pip? It also makes no sense why it would only work on 1 action, but that is all I can come up with, or there is an extra effect to PB/Masterful Blitzes we do not know about.