Final Fantasy V. Give it the 3DS and/ or Switch treatment with a touch of upgraded graphics and sound and with the GBA's translatation
Final Fantasy VIII. Give more foreshadowing towards future events, give other characters more sidequests and growth. Irvine stops womanizing, Selphie calms down a tad, Zell becomes some sort of a Balamb Garden leader, Quistis moves on from Squall and helps around Balamb. Rinoa needs to be saved once and that's with Adel. Seifer redeems and teams up with Squall and Rinoa to help defeat Ulti, while the others battle a big bad monster somewhere else within Ulti's castle. Have Ellone's powers explained better and have Edea stay as a party member.
Chrono Cross. Dump alot of the optional characters and just focus on a select few. Have the story center around them.
Crisis Core. Dump Genesis. Holy mother of grass. Make Cloud, Aerith, Sephiroth, Tseng and Angeal party members. Make battles feel less repetitive. Get rid of that " gambling " leveling up system. yuck. Aerith is not Yuna- she lives in the slums, give her a dirty dress and a weapon and have her always be careful and a bit paranoid of the Turks watching her.
Ehrgeiz. Give it the Soul Calibur format and a much larger cast of characters.
Originally Posted by OP
The only catch is that you can only choose one game per franchise (spin-offs included) so you can't just name off three FF games and two Kingdom Heart titles.
Oh whoops ! Okay, remove FF VIII and Crisis Core. And put in Dragon Quest V ( would love to see a DQ XI treatment of this ) and copy that Legend of Dragoon idea Lone Wolf Leonhart had.