While the parallels in advertising between the boys with the dogs and each getting a galar fossil may be isolated incidents, there are a couple twin Gen8 pokemon that I am curious about, namely the Applin branches, and the alternate forms of Urshifu and Toxtricity.
Ash likely wont get a Toxtricity, and neither Applin evolution seems popular enough that the writers would further expand Ash's rotation team with one. I could see Goh joining Ash on the tower trials as another story arc, alternatively Ash takes it with one of his rivals/ fights Mustard with the other form.
I think that they would evolve in the arc/ episode and not remain a Kubfu for long because of the series episodic nature.
My one reservation with this is that while Bea may turn out to be Ash's main rival outside of the masters 8 (and he still has past rivals showing up), it's allot of investment into one single opponent.
There is the Lucario and Grapploct rivalry, Pikachu and Farfetch'd may want redemption, then you tackle on Ash and Bea having Urshifu. While it looks like Ash will have a rotating team, I wouldn't want them to invest too many pokemon into one opponent.