I mean they totally can they are already fucking around with the existance of wyrdeer and basculegion i really wonder how the home update will handle it
>They can just put them under the (?) region like meltan and melmetal and just make them pokemon 899 and 900
>They can make Hisui count as it's own region and have it be the region with the smallest number of pokemon ever
>or they could put them next to arceus as the new 494 and 495 but that would be dumb and would make wikis mad
so even if it's just acient sinnoh hisui should be seen as it's own region