GB:
Gen 1 had yellow as third version and Gen 2 as a sequel.
GBA:
Gen III had emerald as third version and FRLG as remakes
DS:
Gen IV had platinum as third version and then HGSS as remakes.
Gen V had a set (sequel) as third version.
No need to make a sequel of GBA games because unless for the DSi, they were still playable and compatible. No need to make remakes as V gen because it's on the same console.
3DS:
Gen VI didn't have third versions, ORAS as remakes.
Gen VII will have Ultras, a set, as third versions.
GBA games couldn't be played on the 3ds, DS games can. If you look at this angle, which I don't like and don't agree with, and don't take into consideration virtual consoles, the only gen that needs a remake is Gen 1, unless they consider Gen 2's Kanto to be sufficient.
This seems to be GF's point of view. My opinion is that since we have 3ds models and an engine, instead of having remakes, we should have new games, sequels, for every region using those models, with updates that makes possible to play one region against another. This way we could have XY or a sequel that could play against Alola and so on. This would make possible to have new generations and regions using the lazy man's work to make everything compatible.
