According to this Tweet, various Pokemon game listings are shown for the Nintendo 3DS. Most notably, two slots called "VERSUIB_CALOS_RESERVE3" and "VERSION_CALOS_RESERVE4" are present. "Calos" seems to be based on the word "Kalos," which is the setting for Pokemon X and Y. The game names appear before Sun and Moon, providing evidence to the fact that Game Freak had at one point considered making proper sequels to Pokemon X and Y. The fact that there are two game IDs also makes it more probable that the games were more likely going to be Pokemon X2 and Y2 rather than a unified game like a Pokemon Z, but no titles are officially confirmed.
ÚLTIMA HORA: Filtración del código fuente de USUM confirma que inicialmente Game Freak reservó espacio para dos juegos adicionales ubicados en Kalos, aunque los planes nunca se materializaron. pic.twitter.com/4KnZipcBnf— Centro Pokémon (@CentroPokemon) October 17, 2020