User blog comment:Flameflire/Ash's Future Pokemon/@comment-44688178-20191227095923

Can anyone see a common theme that has been running in the anime for a while now?

The ones I can see are:

Since Unova he has obtained at least one Dark type by the end of the series

He tends to get a type he hasn't gotten before :

Sinnoh - Dragon

Unova - Dark

Kalos - N/A (Though he did fully evolve a pseudo legendary, that's not the same thing)

Alola - Steel