Done my first 15 matches. What I've seen so far
-zero double primal teams
-a few variations of big 6, the closest resemblance replacing Mega Mence with Cress
-a few RayOgre teams
-two teams with Xerneas that weren't big 6
-three teams with Ray that weren't RayOgre
-one Yveltal but it wasn't on a dark spam team; it was paired with Primal Groudon
-sadly about half the teams I've seen are from people not well acquainted with the tier sadly. More than the last IC. In part because I had difficulty finding opponents for my last 5 matches. I saw a team with Gastrodon, Sylveon, Cradily, Aegislash, and female Meowstic. And yes there were only 5 Pokemon on that team.
Summary of the legendaries I've seen in order of most frequent: Primal Groudon, Rayquaza, Xerneas, Primal Kyogre, and tied Yveltlal and Reshiram (the latter on a questionable team)
I've faced more Mega Ray and Mega Mence than Mega Kang this format - i've only faced one Mega Kang so far. No Mega Gengars or Mawiles. I've also seen Mega Gard, Mega Zard X and Mega Audino on not-so-good teams.