Granted it won't be completely straight forward for every class, but there are still numerous ways it could be implemented in PVE.
Being able to consolidate combos would drastically reduce the amount of finger gymnastics and separate hotkeys we would need, though.

Just brainstorming some ideas here, but let us set a hotkey as a consolidated button, then load in which abilities in which order we want them to be used.

E.G. Warriors can set up a consolidation key for the Butcher's Block Combo, a consolidation key for Maim + Storms Eye and leave Storms path as a separate hotkey cutting down 6 hotkeys to 3 hotkeys.

Monks can set up a consolidation key for flank weapon skills and a consolidation key for rear weapon skills, but it would change both based on stance so that they can still use whichever is most beneficial for the moment. 6 hot keys become 2.

This would allow us to use more hotkeys in more accessible locations for off GCD abilities.