Here's what I would and would not liek to see.
1) Active Time Battle must stay, completeylyl unchanged.
2) the battle swirl (and battle maps" feature need ot stay as well. However, more battle maps, such as ones with stairs, for example, coudl be made.)
3) the gourad shaded look should be kept for many monsterrs. Maybe add bump mappig for texturing, but the graphical style of the enemy monsters shoudl be retained. The FPS, however, could easily got up to 60 now. And of course the battle and field models of the characers wold get an improvement.
4) extra content, such a s optional side quests, more Weapons, etc. Maybe a new materia or two.
5) better translation.
(examples. PCS instead of PHS in the us version. you see PHS was a play on "personal handifone system" in japan, and to carry the joke properly, here, it wuld be (SPrint) PCS (maybe even with sprit logo!).)
6) a bit of rebalancing, and perhaps aslight difficulty increase. the game really is a bit too easy, thugh in the beginning that's not a bad thing, but when youget onto the world map it really shoudl kick up a notch or two.
7) Musics soudl get a quality upgrade, but many of the tunes are great as is and hod up today. Wisely chosen sample improvements will make thme better, but overdoing the sprucing up will ruin them. Take Makou REactor XG fora good example on how to improve a tune.
New Game Plus. EIther use the Chrono trigger styele, wher it's jsut gravy, andlets you get waht you missed the first time, or the Parasite Eve style, where you get to go for the TRUE ending, with difficulty kicked up a HUGE amount.
ANd what i DON'T want to see.
1) Aerith ressurection (she will ALWAYS be Aerith to me). no no no! this is a scene breaker. But maybe it would be okay as a part of a difficulty enhanced new game plus, liek parasite eves, where the true objective is to bring back Aeris, and recover th Holy materia (which oddly enough is stolen when Aerith is killedthis time thru, and yo have ot go through LOTS of trouble to get it back)