I'd love to see something similar to Vincent from FFVII where you could transform into different beasts. Seeing how Reaper can change forms when it merges with the voidsent, I know there could be some kind of way to implement this. Maybe this could be a future Beastmaster job. Instead of taming monsters to fight for it, it becomes the beast itself. Maybe that's more similar to Gau from FFVI?

I'd also love to see a job with a double-sided blade like Zidane from FFXI. Not sure what it would be exactly since Rouge/Ninja is already implemented.

A lot of people have been asking for a Mystic Knight for the longest. It could work as a tank if it's anything how Celes plays in FFVI. Using the runic ability to absorb damage and counter it or protect allies.