Is Pokemon Sun and Moon's story new or a continuation?
Firstly, there is a drastic change in art style compared to the XY&amp;Z series. Also, Ash is depicted more as a comedic character compared to his character in XY&amp;Z. One interesting factor to note here is that unlike all the other series before, anything related to Kalos or Ash's adventure there hasn't been mentioned even once.

However, based on Pikachu's move set, we know for sure that it's post Unova. And another interesting thing to note is during the episode where the characters visit Kanto, during the battle between Brock and Kiawe. Ash had prior knowledge on Mega evolutions while the rest of the characters didn't know what it was. Ash came to know of the same during his time in Kalos.

I guess it's up to to the writers to decide based on how they want to continue the series in the future.