I was guessing we'd get a Celebi Prism Star at some stage, and I'm glad, though the question now is whether it'll be more interesting a card than Shining Celebi.
Also not surprised about Tyranitar-GX - I suspect it'll be a dark-type as there has yet to be a Stage-2 Dark-type GX, though hopefully it's playable compared to the Tyranitars we got back in XY Ancient Origins and Fates Collide.
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 Fighting Type could be a very good addition to the set, i bet to Feraligatr-GX, Donphan-GX and Maybe some Another Prism Star like Unown.