I think you could encourage formations through weighted characters - monsters have collision, players have collision.
Then follow that system up with monsters that have moving spells (pushing, pulling, leaping, tossing - when logical, dont do it for shits and giggles), spells that are projectile (mortar spell that arcs and does aoe, or a line spell that hits the first target and some may penetrate), combine with terrain, weighted animations or no animation lock, and you'd have a pretty varied battle field imo. Add a hold stance / block ability (reduces movement spells effects and increases block/parry chance (*) at the cost of TP - ensure blocking is timed and not held down or repeatedly tapped without cause). Shields could have a much more responsive effect to blocking ability - making Paladins block quite distinct from a BLM holding their staff up, perhaps build it in as a passive to the GLD.
Paladins blocking fireballs and blocking enemy movement eating charges in the face while holding their shields up, mages dodging mortar attacks and monsters leaping over the front lines, perhaps even leaping over to toss the mages into a circle of other monsters (smarter AI) - or positioning themselves so they can cast gust and toss your whole party over the cliff..
I worry that having these formations (OP) giving bonuses that players will then just calculate the best formation for their setup and maintain that one (basically making a static party in a pretty shape).
Talking about pretty shapes your picture is pretty sexy