I was just wondering, depending on how summons get implemented, maybe this is a good idea:
After going through some process of collecting summonable creatures ( Quest/Battle/Ranking up a Summoner Class), the character gains an Action to summon each individual creature.
Whether or not you can equip multiple Summons, or whether other classes can summon doesn't really matter to me, but it would be fun to summon on other classes.
After hitting the action for say, Titan, the character plays a fancy summoning animation and is locked in place or phased out. Then the player takes control of his summon and has available a slew of new abilities specific to their summon.