I'd honestly enjoy a starting party choice much like you got in the original FF. That pretty much settled things, and you can throw in as many guests as you want. The only issue would be writing adaptive storylines with the different combinations of characters, but that could just be changed by labeling them as character 1/2/3/4 in the story progression, choose gender on that basis, and add little quips depending on what class they are, and side cut-scenes.
With that formula in mind, i think they could work it out by not having to change a story they've made, but the character manages to make a proper party, as opposed to what FF has devolved where by the time you've completed the game 100% every character has the same moves, and the same strategy in fight; target, attack, rinse, repeat.
I'd like them to make fighting interesting, and stop pandering to players to allow them to do EVERYTHING the first time they go through the game.