It's not really wait and see kind of thing though, as first off it doesn't make any sense to introduce a new Alolan form in a region other then Alola and if they were to introduce a new regional variant in Kanto it would be a Kantonian form of a pokemon from another region other then Kanto, also if Vaporeon were to get a new regional form then Jolteon and Flareon would likely get one as well since they are considered a trio of sorts, and also a dead give away that this is fake is the fact that this supposed Alolan Vaporeon is a pure Water type and if you do simply research you will see that when it comes to Alolan Forms that they are never the exact same type as their Kantonian counterparts, what I mean by this is while it's true that some of them may keep part of their original typing it's also true that they either change their typing completely or add a additional type, so if we were to get an Alolan Vaporeon there is no way it would be a pure Water type since Kantonian Vaporeon is a pure Water type.
Also as for the whole thing that Ash always has to have a Grass, Fire, and Water type pokemon in every region he goes to, this has already been disproven by the fact that Ash didn't get a single Grass type pokemon in Kalos, so it's entirely possible that he could skip out on getting a Water type pokemon in this region. Is it possible that he could get a Water type pokemon this region? Yes, but it's not a guaranteed thing to happen and at this point it seems likely that he is probably not going to get a Water type this region.
Also thanks to the datamined from Pokemon Quest we know that the new pokemon is a actual new pokemon and not a regional variant or form of an existing pokemon because in Pokemon Quest there is a spot for a pokemon with 808 on the national dex with that being the last slot with a actual number meaning the new pokemon being introduce in Let's Go Pikachu and Let's Go Eevee is going to be number 808 in the National Dex, meaning there is no way that it's going to be a new form or regional variant of Vaporeon.