As it stands, it has exceptionally few uses - IE, accidentally dropping Astral when at 0 MP and getting back enough MP to cast a Blizzard spell, and... Nothing else, as it's old aggro management was removed for ShB.
The problem is that it's a role skill for casters - who have very few as it is, and it's near useless on one of them.
For the uninitiated, BLM's stances of Astral Fire and Umbral Ice block MP-refresh effects, which includes Lucid Dreaming now, included old Ewer and... the Ranged Physical skill which the name of is eluding me (I think it was actually Refresh?) - not that you needed any of them anyway, as Umbral restores a vast % of your total MP per tick.
I personally want Manashift back for at least BLM. It should be free to use, and a two minute cooldown sounds appropriate - but even then it still wouldn't be overpowered as you'd need to take attention away from your Fire 4 victim for a second or two to support an ally. I could still see it mostly being used in a real emergency or if you took BLM into new content like a crazy person.
I wanna be said crazy person but it's a little unfair to be selfish to others like that, so I usually take RDM instead for the first few days. :/