The majority of jobs use either MP or TP.

The only jobs that use both are PLD, DRK, BRD and RDM.

PLD and DRK only use TP for their melee combo.

BRD only uses MP for Foes Requiem

RDM is the one that will probably be most effected ny the change, using both MP and TP for their core rotation.

But most of these issues are already solved if single target melee attacks simply have no cost at all, given that their current TP costs don't really have any effect anyway.
It's only AoE rotations that have a cost to prevent endless spam, DRK's is MP already, do the same for PLD and RDM's AoEs, and its just Foes Requiem we need to worry about.