What if, and I'm not sure if this is possible to do outside of what happened in Dissidia, but what if there was End Game content where you could challenge either heroes or villains of past Final Fantasy games in battlefields in order to obtain Armor and/or weapons inspired by them? No big questlines. Just battles.

For example, after fulfilling certain requirements, you could go and battle a FFXIV version of Shadow Lord from XI! Or, if possible, even villains like Kefka and Golbez. Perhaps heroes like Bartz or Squall.

Of course, they wouldn't be easy. Still, wouldn't it be a cool idea to fight "visions" of these characters for not only the fun of it, but inspired gear?

And again, even if it's not possible for all Final Fantasy games, having guest battles from FFXI alone would be amazing. Shadow Lord, Eald'narche, Promathia, maybe even Prishe and Naja Salaheem.

Shantotto perhaps?

Anyway, just a random idea I thought of and put down here.