I have a feeling that the Journeys series is backing out from its "multi-regional" format. I mean, they are not even trying to reference past games and series anymore.
First we got the Cresselia/Darkrai two-parter set in some random unnamed town in Sinnoh, now they're giving us some non-existent "Eclipse Castle" location and calling it Johto. The "Uninhabited Alola Island" that we're getting in the upcoming episode seems to be an example of that as well.
I know that the anime always tended to create new locations that don't exist in the games (and if it was a revisit to one of those already-created places, I would fully appreciate it), but this is not the way to go if this series wants to maintain its "multi-regional" feel. Creating some random location (that could be located just anywhere) and saying "Hey Goh, we're not in Kanto anymore" seems like the laziest and most anticlimatic way to feature Johto, or any other region for that matter, as it doesn't feel like a revisit at all. The fact that it features Espeon and Umbreon doesn't help things either, as those aren't really "quintessential Johto Pokemon", being evolutions of Kanto-introduced Eevee. No need to feature Johto just for that.
I know it is not a big loss, since the Journeys did everything to make those references seem lackluster and blue-balled (like Vermillion Gym without Surge; Hoenn Battle Frontier without... well, Battle Frontier; Pewter City with no sight of Brock; or some boring Mauville outskirts acting just as a background for an unrelated story [what a wasted chance to explore ORAS-style Mauville...]), but I feel that they're not trying anymore. They're just slapping random things and calling it [region].
As for the episode, I never liked the doppelganger cliche. But I guess this episode will be a kind of setup for Chloe's Eevee evolution and probably Goh will catch a bunch of Johto Pokemon. Fair enough, but I would expect better from a Johto-based episode.