Actually, I've been thinking of this and never understood why is it not done...

In my view, it would be a great idea to introduce special summons that require special chases (e.g: 35/50 combo hit) and cause a lot of damage or more buffs/debuffs. A fast exaple: When there is a 35 combo hit you can summon kurama, who causes heavy damage and ignition to up to 6 enemies. Of course they need to be great summons such as tailed beasts or new ones but still amazing. Perhaphs its not the best example but i think It'd be a good idea.

Another possibility is that they chase 2 conditions... for example: chases the high floated -AND- poison and causes knockdown, paralysis and ignition. These adds new and better strategies and ways to arrenge your team.
It's just an idea... I hope you like it and if possible add it. I'd love to play with these big summons.