I've actually had the idea for a long time. With recent...additions, it's been refined, of course, but the basic idea is still there. Equipping certain combinations of spells give us traits, these and the statistical bonuses we usually get from spells tend to reflect the class of spell they represent. It's like a game of tug of war, each side asserting their power over the whole. What if this concept were taken further? What if you allowed that part of the beast a little more dominance to gain more of its power?
Stance JAs, unlocked by a certain combination of spells, for each of the main roles in a PT: Physical DD, Nuker, Healer, Support, and Tank. Each enhancing the spells they represent at the cost of weakening the others.
In the case of physical DD, it would be much like a mix of Hasso & Art in that it would lower the MP cost and recast while also giving modest boosts to attack, blue attack, accuracy, auto-attack speed, and the damage multiplier. As a consequence, nuking and healing spells take a reduction in recast and increase in MP cost. This would improve BLU in merit and HNM by making spells more efficient while not making them drastically more powerful all the time (though odds are good it would be the most common stance.) BLUs would have a greater use of their auto attack and more efficient use of their physical spells without totally breaking them. In merits, BLUs would still use multi-hits over the higher maintenance CB & VC. In HNM, CB & VC would still be more powerful than the multi-hits and would be more easily spammable (it may also improve lower level spells enough to get them more use in both areas as stop gaps).