Charmna would completely defeat the purpose of battling NMs that have a primary characteristic of charming. There are so few mobs that actually have a threatening charm anymore that it would just be an unnecessary buff. IMO, it would further remove strategy from mobs that one required it in certain situations (e.g. duoing Cirein-croin with a tank + mage,) If it were introduced, it should have properties similar to Cursna versus Doom, where the removal isn't guaranteed.
Amnesia-na would be far more appropriate in a sense that Amnesia doesn't pose nearly the same amount of threat as charm(ga). Amnesia just ends up drawing out fights that're unnecessarily long due to either an amnesia aura or a move that inflicts it. Unless coupled with single target hate resets, all it does is make some fights longer. Also, Amnesia-na is technically in the game already, but who carries
these around anymore?
edit: Revivscence would be awesome. It should be granted by an item though, like Impact/Twilight Cloak! :O