The one thing I would like to see is jobs. The last single player FF to use jobs was X, and even then you can make everyone eventually learn everything. I enjoyed FFXIII more when they all had three 'jobs' each, then it got to the point where it was just "oh screw, make them learn whatever you want".

A system like IX would be great, where you had one thief, one black mage, one dragoon etc. It makes the characters more unique.