I feel like they would make a Kanto based game due to all the show gen 1 pokemon get in x & y, but I think it should be not a fire red/leaf green remake but a whole new adventure together taking place after x & Y in the pokemon time line. It would be a great way to spruce up the Kanto region which is war torn since time heals. Call it pokemon purple version with the mascot being mewtwo, and to add you need 16 badges not 8 so you can go johto from Kanto. The regional dex would have gen 1& 2 pokemon as well as certain gen 4 pokemon such as magmortar evolved from of gen 1 pokemon magmar and honchkrow the evolved from of murkrow and sylveon from gen 6 since it is an eveelution. It would also give megas to the johto starters you could receive in Kanto like the Kanto starters in kalos. Here would be the gym leaders in order (each will have 4 pokemon to make it harder than x & y) :
Brock- type rock- pokemon: onix, geodude, kabuto/omanyte, aerodactyl / mega aerodactyl
Misty- type water- pokemon: psyduck, staryu, lapras, starmie
Lt. Surge- type electric- pokemon: voltorb, magneton, electabuzz, raichu
Erika- type grass- pokemon: leafeon, victreebel, Vileplume, tangrowth
Janie- type poison- pokemon: arbok, golbat, venomoth, weezing
Sabrina- type psychic- pokemon: espeon, mr.mine, xatu, alakazam/ mega alakazam (it would make sense to have some johto pokemon due to saffron city being the town that connects to johto)
Blaine- type fire- pokemon: magmar, rapidash, ninetails, magmortar
Blue- various types- pokemon: exeggutor, arcanine, gyarados, rhyperior
Whitney (connected from saffron city)- type normal- pokemon: blissey, ursaring, girafarig, miltank
Bugsy- type bug- pokemon: shuckle, yanmega, pinsir, heracross/ mega heracross
Falkner- type flying- pokemon: pidgeot, noctowl, farfetch'd/ mega farfetch'd, gliscor
Morty- type ghost- pokemon: haunter, mismagius, misdreavis, gengar/ mega gengar
Chuck- type fighting- pokemon: poliwrath, primeape, hitmontop, machamp
Jasmine- type steel- pokemon: scizor/ mega scizor, magnezone, skarmory, steelix
Lorelei (since pryce retired)- type ice- pokemon: cloyster, dewgong, jynx/ mega jynx, mamoswine
Lyra (female protagonist)- type ground- pokemon: golem, dugtrio, donphan/ mega donphan, quagsire
Elite 4
Clair-type dragon- pokemon:aerodactyl, gyarados, ampharos/ mega ampharos, dragonite, kingdra
Will- type fairy (to further introduce the new type)- pokemon: clefable, granbull, azumaril, sylveon, togekiss
Koga- type poison- pokemon: nidoking, tentacruel, muk, ariados, crobat
Karen- type dark- pokemon: umbreon, weavile, honchkrow, houndoom, tyranitar/ mega tyranitar
Champion Ethan (from heartgold/ soulsilver since he beat champion Lance and red)
Pokemon: electivire, meganium, typhlosion, feraligatr, donphan, dragonite/ mega dragonite
The bad guys would be team splicer mostly run by scientists whose goal is to successfully clone Pokemon from dead Pokemon they play on the emotions of people who lost their Pokemon to death they are radical scientist not not associated with the rest of the scientific community in the Pokemon world and therefore need to do various schemes to fund thier research they are also trying to make other Pokemon that normally can't mega evolve mega evolve. These scientists were there on Cinnabar Island when experimenting with mew. There grunts for being people who are brainwashed by them believing that what they're doing is possible and ethical research. In fact each grunt has a dear loved pokemon lost to death. And in the battle frontier silver could replace palmer in the battle tower. Lance & Bruno tried to kick Will out of the elite 4 but with his new fairy type he beat both of tthem. after Caitlin left the battle frontier to be the unova elite 4 the duo broke up and someone have to fill it in so Bruno and Lance filled it upthe battle castle collapsed inorder to create the battle Coliseumso that's why in black and white, black and white 2, and X & Y there was no battle frontier