There are 32 reasonably accessible non-meta keys with the left hand on all QWERTY keyboards. Some keyboards have additional access but have you reaching into the right-hand area.
However:
Some of those aren't really usable for actions: ESC, CAPS, TAB (3)
Some are needed for targeting: F1-F6 (6)
Some are needed for movement: WASD, SPACE (5)
Leaving us with: ~, 1, 2, 3, 4, 5, 6, Q, E, R, T, F, G, Z, X, C, V, B (18)
You need a certain number of actions for non-combat things: mounting, etc. This is up to the player.
It's also inaccessible to force more than two buttons to be pressed with a single hand at the same time. You might be able to do it, but not everyone can, comfortably.
That leaves us with 18 unmodified and 18 modified buttons, for a total of 36 for everything. If you reserve just 4 for non-combat purposes, that leaves you with a cap of 32 actions.
That said, I don't think you really need 32 buttons to make a meaningful rotation based on playing other MMOs and even PvP in this one. We do have some jobs that push right up to that limit, and I think a couple that push past it. Honestly, I would like to see a hard cap of 32 actions per job, if not a little bit lower.
I do think that if SE got rid of the role actions and replaced them with individual job actions, they could free up a lot of button and design space as well as separate the jobs more in terms of design space.
