As it currently stands MP might as well not even be there. No job requires MP management, unless resurrections are required. Removing MP from casters would change nothing, because they never run out anyways - or in case of BLM run out at a set pace.
Simply adding MP cost to every skill and ability of every job will not make jobs more fun to play, if that cost is not relevant in some form.
Also running out of MP would not be fun. If it does happen for whatever reason, the player would be forced to just sit there and wait. Which means there would have to be some way to regain MP for every single job.
Jobs are already way too similar to each other, and recent changes to BLM show the team is not even done with homogenization yet. Having a universal requirement for MP regeneration in some form would just homogenize them even more.
