I was thinking just about that... And had some really "ambitious" ideas. The aetherical mimicry spell would put you into a specific role, thus flagging you as either tank/dps/heal. When you do that, only specific spells to that role would be available. It would be a MAJOR commitment for them to tune a job like this though.

Maybe a meter would be good, but I really thought about the "resource system" being an elemental wheel, inspired on the Eureka one, that you rotate using your "filler" spells, and choose the stronger spells based on the opposite element of the wheel, or something like that. This would do well with the apparent lack of "theme" on the job's flavor, since it brings all sorts of different spells.