New Eeveelution Has Already Been Practically Confirmed By The Anime

thegamer.com:

There hasn’t been a new Eeveelution since Sylveon was introduced in X & Y, but it seems like that’s about to change. While many were disappointed that Gen 8 broke the pattern established by new Eeveelutions in Gens 2, 4, and 6, it turns out there’s a far more consistent way to determine when a new Eeveelution is coming. The Pokemon anime has always told us when to expect a new form for Eevee, and the newest season has been setting up a Gen 9 Eeveelution for quite some time.

If you’ve been watching Pokemon Master Journeys on Netflix (and you should be) then you’re already familiar with Chloe, Professor Cerise’s daughter. Chloe was mostly a background character throughout the previous season, Pokemon Journeys, but she joined Ash and Goh as a main character starting in Pokemon Master Journeys when she met her partner Pokemon, Eevee.

Related: Lance Cheated His Way Into The Elite Four And Tried To Do A Genocide

This is all you really need to know about what Master Journeys is setting up. Every time a main character catches an Eevee it eventually evolves into the newest form. This has happened consistently throughout Pokemon history. Serena’s Eevee evolved into Sylveon in the the X & Y series, May’s Eevee evolved into Glaceon in the Diamond & Pearl series, and Gary’s Eevee evolved into Umbreon in the original series. A side character named Sakura from the original series also had an Eevee that evolved into an Espeon. We never saw an Eevee evolve into a Leafeon, but this doesn’t break the pattern. What matters here is that every time a main character has caught an Eevee it has evolved into a new form.

Pokemon has been known to subvert expectations from time to time - to put it mildly - so that fact alone might not be enough