The set will release in Japan on June 1st. It will feature 96 cards, excluding the 2,000 secret rares. The set will then release in America in August under a different name (because that Japanese name is just odd).
The set’s mascot is Rayquaza-GX, which means this will be our Hoenn set! The current USUM block has been featuring a past region in each set. SM6 Forbidden Light was our Kalos set while SM5 Ultra Sun & Ultra Moon was our Sinnoh set. This now leaves a potential Kanto, Johto, and Unova set. As I predicted during the Legendary Year of Pokemon reveal:
The next TCG set would be released in August, and judging by the distributions of Groudon, Kyogre, Latios, and Latias in that two-month span, it’ll probably be — you guessed it — a Hoenn set!
The next TCG set would then hit store shelves in November, but October and November feature Reshiram, Zekrom, Ho-Oh, and Lugia, which of course are Legendary duos from two different generations. Raikou and Entei from Johto are releasing in April while Tornadus and Thundurus from Unova are releasing in July. So November could either be a Unova set or a Johto set. My bet would be on Unova.
This would leave out Kanto and Johto sets. Depending on when Gen VIII comes out, they will either tackle those two sets in February and May 2019 or just forget about them and start their Gen VIII sets instead (the first two gens have been featured a lot in the past anyway).
Update: I just noticed the booster pack also features an angry Stakataka behind Rayquaza! This means Stakataka-GX will also be in the set!
Japan will also release “GX Starter Decks” on July 13th. There will be nine decks in total, each featuring one of the nine Pokemon TCG types and a Pokemon-GX to match: Lurantis-GX, Charizard-GX, Lapras-GX, Raichu-GX, Mewtwo-GX, Lycanroc-GX, Yveltal-GX, Metagross-GX, or Xerneas-GX. Each deck will come with 60 cards and cost 500 yen (about $5). It is currently unknown if the cards will be straight-up reprints or alternate art reprints.
Thanks goes to Bangiras for the translations!