Is there anything that comes from other games that you'd like to see in FFXIV? It doesn't even have to be from other MMORPGs, it can be from any type of games.
Personally, I'd like to see a mini-game that involves something like Romance of Three Kingdoms style strategy war game. Maybe there's an army officer type of NPC where you can get repeatable quests from, and then you'd get rewarded with points to unlock the war game, the battles in the war game, maybe even characters/units for the war game, and probably decent gear too. It'd be quite a fun way to break out of the normal FFXIV play cycle while still being rewarding.