I'd probably make a Final Fantasy All the Bravest that wasn't just DLC: The Game. I like the idea they had in mind for the game, a cross over game that let you build your dream party, but just playing the game is more of an investment than any recent EA/Capcom game, and to what end?
I'd probably give the game it's own protagonists and give them the Final Fantasy Dimensions battle system, since I liked the Fusion Skills, the increased customization of the characters over FF3 and FF5 and the fact that IT AND 4 ARE THE ONLY GAMES THAT LET YOU HAVE A 5 PERSON PARTY! And then I'd throw in a ton of optional party members from Final Fantasy 2-13. I'd prefer it be done in the 25th Anniversary PSP style and I'd put in remixes from each of the games that'd fit the style, so I guess it'd be done by whoever did the soundtracks for the PSP games. As for the story, I haven't the slightest, I guess that old trope of kingdoms vs empires but the empire being a race of people from the void trying to steal the crystals to sustain the chaotic nature of their world? Pullin' this outta my a** but I'd play it.