I'm all for this. We NEED to reduce button bloat. I'm well beyond the number of keys I can press without looking down at the keyboard or else moving my left hand away from "home position." I have several abilities I basically just click on and don't assign a hotkey at all. And of course, controller players have a hard limit they can't go beyond. We can't get new skills every expansion and expect them to just magically "fit in" without some pruning to make room for them.

I know it doesn't work equally well for all jobs, as some have non-linear rotations. But I still think there's some potential to cut unnecessary hotbar real estate in many cases.

For example, Samurai's three combos. We don't need the final move in each combo to be it's own separate key. It can be the same "Finisher" key, but just change what the skill becomes depending on what stage of the combo you're on -- just like how your Iaijutsu changes to a different skill depending how many Sen you have built up. So, you would go:
1 --> Finisher
1 --> 2 --> Finisher
1 --> 3 --> Finisher

We've just cut two whole buttons from the hotbar, with no loss of utility or complexity. You gotta ask yourself, why was Kaiten removed when this option was on the table the whole time?