Update Character, Armor, Weapon textures from AAR and some HW
Update Character animations (especially for Elezen, its been 8 years now)
Update Chocobo companions. (Better Ai, Flat Stat Boost and New Caster Style)
Update Grand Company Ranks, Give us more higher level armor and weapons for Seals
Update Squadrons with new classes and skills, Increase the cap to 70.
Update the Inventory system, when maxed out, you really do not need 3 full bags for quest items, remove 2 and add them to the normal inventory.

And most of all, START TO WORK ON A NEW ENGINE THAT CAN HANDLE THINGS IN THE FUTURE BETTER.