I would LOVE to have more 'conditional' buttons that hold 3 or 4 abilities on them actually, like how Red Mage and Summoner reuse buttons for several different phases of their rotation. It doesn't even have to be big stuff on the same scale as that. Stuff like making Hypercharge turn into Heat Blast once you use it. Replace AoE actions with a stance that changes your single target stuff to your AoE actions.

As has been mentioned plenty of times I also wouldn't mind getting single button combos like in PvP, but I know that's more controversial.

Something I haven't seen mentioned before though is the potential of jobs getting traits that upgrade role skills into unique abilities that still maintain their original function, but still have some other use as well. Would be a good way to add a lot more depth to the actions without increasing button bloat.

We could easily add a dozen or more skills and still take up LESS buttons than we currently do, if they just applied them we'll. There is no reason to waste an entire button slot on something that can only be pressed directly after something else, and is useless in all other contexts.