"As an aside, the TCG still hasn’t given us any clues about when the Pokemon Switch game will release. However, as I explained in this news story, we know from the Legendary Pokemon video game distributions this year that Japan’s next TCG set will probably feature Unova." - PokeBeach
I feel SM8 would more likely be a Johto inspired set given that Lugia and Ho-oh are distributed on the month of the release of the English SM8 set, like the 3 previous sets before it.
Now that we know of Dragon Majesty, I think Reshiram/Zekrom's month will be focusing on that. I can just picture seeing Reshiram/Zekrom Dragon Majesty promo box(es) containing promos of Reshiram GX (omitted from the main set) and Zekrom GX (we have heard of it's existence as a Japan promo).
Also I'd like to add that a Johto inspired set for November would likely include Lugia GX. This set will also likely combine with SM7a so that would bring Lugia and Zeroara together in a set (making the assumption here that there is no Lugia in SM7a), and as the mascots no doubt. Based on the timeline of previous movie releases, Movie 21 should release internationally around the same time as this set. So it all pieces nicely.