No, the next games arent the diamond and pearl remakes, GameFreak doesnt want the next game to be widly incompatible with the previous installment (thanks to the lack of national pokedex). The next games will be the enhanced version of sword and shield.

GameFreak considered not making any more remakes since the design philosophy of the games is redically diferent but fans seem to want them way too much to not take the business oportunity.

There is some serious talk about using the lets go branch of the engine for the remakes since the square mapping benefits from it. it seems like theyre dead set on it.