Comparing FFVII, where anyone can use the summon materia and summon a creature, or FFX, where only one person can summon. How about them using a system where there is a new character class, with something like vincent from FFVII. They could have 3 or 4 people who, instead of summoning an outside creature, have the ability to transform into a more powerful creature with limited moves. They could have a person with elemental-based transformations, a person with different kinds of attack type transformations (something like a piercing, blunt, or aggravated attack), etc. It would make it so that you could actually fight people who can do the same. FFX had you fight other summoners, but they were far apart and not that much of a challenge. well, whaddya think???