According to the set description, it will feature Rowlet & Alolan Exeggutor-GX, Mew & Mewtwo-GX, Espeon & Deoxys-GX, Umbreon & Darkrai-GX, and Garchomp & Giratina-GX.
Out of those, only Rowlet & Alolan Exeggutor-GX was unknown until now. It will probably come from Sky Legend since Rowlet flies and Alolan Exeggutor is up in the air.
By extension, Unified Minds should also feature Raichu & Alolan Raichu-GX, Heatran-GX, Mawile-GX, and (probably) Articuno, Zapdos, & Moltres-GX.
There will be eight Tag Team cards, nine additional Pokemon-GX, more than 25 Trainer cards, and two new Special Energy cards. There are no new Special Energy in Japan yet, so they’ll come from an upcoming Japanese set.
The set will yet again break the record for the largest English set ever, with “over 230 cards.” Lost Thunder featured “over 210 cards” in its set description but 236 cards after secret rares. This means Unified Minds will likely breach 250 cards with its secret rares.
The set’s Elite Trainer Box will feature Mew and Mewtwo.
Unified Minds will be a combination of SM10a GG End (released April 5th in Japan, 69 cards), SM10b Sky Legend (releasing April 26th, will feature 54+ cards), SM11 Miracle Twins (releasing May 31st, 94+ cards), and two upcoming Japanese starter decks (releasing May 31st).
This may be our penultimate Sun & Moon set. We’ll likely get our last English set in November. Then Japan will probably release their first Sword & Shield set in December, which we would get in February. This is assuming the release pattern stays the same as past generations.