- If they're not going to go the pure ATB route, I'd want them to go a semi-action semi-ATB with the battle system.
Let the player run around in battles and have attack, defense and dodging be manual and free, then also have an ATB gauge for each character, which when full, gives you access to materia/items, by for instance pressing triangle. Press the (triangle) button, time slows down - slow-mo or completely - giving the player time to navigate the menus, select targets etc. or even change characters (although that option should be available at all times though, linked to the lower trigger buttons or something).
This way you'll have the mobility and the interactivity of most action games, whilst also having the possibility to keep a complex materia system, multiple commands, and micro-management of your party.
It's the best way I can think of to satisfy both camps and keep the game-play fresh.
- I hope they find some sort of stylistic solution for keeping the world map - either by doing like FF15 and creating a large open world and putting it into segments separated by loading screens so that the entirety of the world can be kept, or by simply being old-school and keeping the traditional world map (perhaps change the scale and presentation a bit to not make it look too out of place).
- I hope they keep up the tradition of breaking up the base game-play with various mini-games, button-prompt events to keep the experience fresh. I also hope they add some new mini-games (maybe fishing or whatever) just because they can, because it extends the experience without hampering its quality or structure.
- I agree that a day-night cycle could be cool and interesting, but I don't think they should put the game on a time limit like the Persona games, because that's really stressful, and annoying. It also punishes players who fail to prioritize their time in game properly, but don't have the time or energy in their real-life to start the game from the beginning over and over again when they find out how they messed up.
- I think they need to give a lot of though to the balancing of the game. Amp up the difficulty level, or at least provide something as basic as a difficulty option that raises the base stats of all the enemies or something to that effect.
Take a leaf out of FF10's book and make sure that all the skills and spells are actually useful at times.
- Ties together with - and will probably only work if they keep - the world map -
Airship, vehicles, Chocobos etc. Keep it in, expand on their use etc.
- More everything : More materia, more equipment (visual equipment that effect the appearance of the characters mind you), more side-quests, more non plot-related locations, NPCs, roads and railroad tracks on the world map/overworld, public transport choices, etc. etc. etc.
That's pretty much it from me.
(it manages to have a powerful story while maintaining an open-world structure, it has a great cast of characters with awesome voice acting, and it's a LOT of fun - I could keep praising this game for ages 
). In that respect, if driving vehicles is a properly implemented game mechanics in the remake, the bike chase could be just a "special episode" using these mechanics (replacing shooting cars from Sleeping Dogs by hack&slash with a Buster Sword).
