Right now we have confirmed from Sm7a: Virizion-GX, Magcargo-GX, Zeraora-GX, Genesect-GX and Ditto. In SM8 will have Lugia-GX (Psychic PLZ!), blacephalon-GX (Ultrabeast, Psy maybe), Tyranitar- GX and Celebi ∆.
Until now we have 7 GX Pokémon and 2 Prism Star, so i think that maybe a Water or...