If Square made a rogue-like dungeon crawling or sand-box RPG Final Fantasy, that would be interesting. To each their own but I still find dungeon crawling to still be fun and sand-box elements can make a game enjoyable to play a second time (ie. Fable II). The first time around I played as a morally pure character (except for the odd pre-marital sex and threesome) and now I'm going through as a 100% corrupt strumpet who sleeps around a ton and becomes filthy rich by buying up all the properties and overcharging people on store prices and rent. I don't want her going on a killing spree just yet because I believe that's going to make it hard for me to go for some of the achievements I'm missing. But I will go on that killing spree and it would be cool if stuff like this was in a Final Fantasy game. Say you go sleep with Rinoa, tell her to piss off for being so needy/clingy, and then slice her up with your gunblade because you caught her cheating on you with Seifer. Now that's my kind of melodrama.
Also I want to see jrpgs return to their open-world roots. You had a lot of freedom of movement on the world map in the early Dragon Quests and Final Fantasy 1. Someone on GameFAQs I believe used a code hack to start with four Lvl 50 Black Belts and he beat the entire game in under an hour. That is how open FF1's world is. You aren't all that restricted in where you can go. It's just that you are unlikely to survive if you try. lol. I've heard that you could go straight to the final boss in DQ1 very quickly if you were feeling lucky. It's not like today where they forbid you to venturing off into places you aren't supposed to be in or they railroad you through a series of linear missions to open up more of the world map.
