I personally think they should bring back some older elements of FF and reintroduce them into a more modern theme. For example what would a red mage look like in the modern world or in a near future world? What kind of weapons would a modern red mage use or what kind of magic would the mage use in the modern world?
I picture a modern world, maybe near future like 20 or 30 years from now. Of course some technology will have to be sci-fi after all this if FF we're talking about. So in this near future world have airships, chocobos, and moogles, ect. As well have a version of the job class system that fits with a near future world. When you look back at the FF series, the Job Class system is always used in worlds based on the past. Sure FFXIII introduced something new like the job Class system with Paradigms, but what I'm talking about is the old job classes designed for a modern/near future world.
As for the leveling up system, we could have Job Classes level up as well as the Weapon level up system of FFII slightly changed for a modern/near future world.