i'm definitely opposed to the idea of using float to get to areas not accessable by any other means. that's just kinda cheesey to me.
and if they were to put float in this game, they would not be "creating" a new spell, they'd be using a spell that has been in virtually every FF since like FFII or something. it's always been a spell that makes characters float just maybe like 2 feet off the ground.
it would let us get over poorly thought of ground like the stairs in Ordelle's caves or Crawlers' nest without giving people access to "Jump" (which i think would be totally annoying)
it could grant immunity to say ground based attacks such as a worms' tremors, but not magic such as stone, since stone attacks the individual wherever they maybe, not necessarily through the ground (i.e. you're able to cast stone on birds and wyrms in the air)
and improving movement speed is a neat idea, but not like flee, that's excessive. more like quickening, i could see that as acceptable.
oh, and the people who cry about "not realistic", you are playing a fantasy game, where cat people and elfs and whatever the fk galka are fight mythical beasts largely through magical means and whatnot, tell me where the "realism" is there. it's a fantasy game to be fantasy, not a fantasy game to be realistic. people being able to float or levitate would be no less realistic than summoning a great avatar to cast spells on your party and fight by your side.