I'm thinking the main thing will just be any of the standard combo skills will just be free and the ones that cost a lot of tp such as AoE will have a mana cost.

Or they could make even those free. They're not a big deal for the current mana classes to maintain aside from healers anyways
and just make it so every dps works somewhat like dark knight with a whole subset of mp using stuff
massive job overhauls has been a staple of expansions anyways