I keep thinking of Dark souls when they mentioned "consolidating TP and MP". The stamina bar in that game is one way I think it could work. Each action uses a certain amount and other factors affected the regen and length of the bar allowing the player to have more actions within a given limit. It allowed for very inclusive gameplay where one stat or equipment could make the difference between you getting three 2h-GS swing vs two 2h-GS swings before bottoming out. It could work in the same way in FFXIV since the TP bar is essentially a very, very slow version of it.