Det. Viper
That’s Detective Viper to you
I was thinking the same thing regarding the regional evolutions. At some point it will be inconvenient to evolve say Pikachu into an Alolan Raichu. So having something to the effect of an Alola Stone to evolve non-regional Pokémon into their regional forms. Having the Alola Stone, Galar Stone and Hisui Stone as super rare items could rectify this.Personally I'd use the Sinnoh Stone from Pokemon Go and just re-purpose it to have the effect that you just need to know the move and use a Sinnoh stone to evolve pokemon like Stantler. This would be an easy way to evolve them in-games where strong style and agile style aren't possible while still tying it back to the region but making it possible to evolve in violet and scarlet