We will see soon enough!

Gen 9 in 2022 with a fairly mixed region with big cities but also ancient areas,
Gen 10 in 2025 with a region based more on tradition, lots of ruins/ ancient areas,
Gen 11 in 2028 with a region that is more tropical, kind of like Hoenn/Alola,
Gen 12 in 2031 with a region that’s mixed but colder than other regions,

Pokémon Black and White remake set for 2026, 2027 if there is a delay.
Pokémon X and Y remakes a bit of a paradox set for 2031 (same year as Gen 12) or 2032 If delayed. Gen 12 is the end of the fire starter pattern anyway so it is possible that Gen 12 is the last generation of Pokémon.

Remix games (Platinum, B2/W2, Us/Um, S/S DLC) will still happen around 3-5 years apart from each other with the last ones happening in either 2027 or 2029.

Fire starters are in pairs, if Gen 9 is a Horse then Gen 10 will be a Goat (or the other way around, Gen 9 Goat then Gen 10 Horse). Same goes for the Snake/Ox starters.

Grass starters will probably keep progressing to more current but still old animals, like more turtles etc,

Small % possibility but Gen 9 starters could be another Grass reptile/turtle like Pokémon, Fire Horse, and a Water Bird, while Gen 12 could be Grass Lizard/Fire Snake/ Water Turtle