Satomine Night
The Power of Z!
I suspect another battle may occur in the long run.
This shown progress, while Pikachu was still obviously outmatched, he managed to knock Tapu Koko back a bit (in the first battle, the Z Move didn't even budge it, here it knocks it back into a tree). Obviously the deity wants to make sure Pikachu gets stronger.
I expect this is also why the battle was somewhat slow paced, Tapu Koko wasn't fully battling, it was testing, it wanted to see what Pikachu would pull off.
I agree. It was pretty clear to me that Tapu Koko was testing Ash and Pikachu, especially when it floated in place, waiting for Ash and Pikachu to use their Z-move, rather than taking advantage of the fact Pikachu was discombobulated to attack again. It wasn't battling with the intention of defeating Ash and Pikachu; it was battling with the intention of testing Ash and Pikachu.
I expect quite a few more battles between Ash/Pikachu and Tapu Koko over the course of this series.