I'm not really seeing any complaints here about how MNK does basically exactly this already, so, not sure why we can't somewhat agree to spreading it to other jobs.

All skills that start a combo always available for restarting any combo. All 2nd/3rd skills in combo unavailable.
After skill 1, any skills that are a part of a combo available after skill 1 can now be used. 3rd skills still unavailable.
After skill 2 of whatever chosen combo, any 3rd skills in that combo are available.

What's so bad about "turning off" any combo skills that aren't highlighted? You literally never use them anyway.