You don't necessarily have to have units just standing around to to ATB or turn based. In FF12 and FF13 positioning was largely irrelevant for most fights (and complete BS for the ones it was, as you don't have any decent way of controlling it for the party) so I don't see why you can't make something turn based where the party and enemy units are moving around dynamically the whole time. It would be complete window dressing, but to be honest most of the in battle character movement is already superfluous to combat mechanics.