Here's what we KNOW about the Hacker's Memory set:
Pic related
More support for the CS deck
The remaining Royal Knights not featured in BT22, plus a new King Drasil
Sistermons (we've seen art of them beating up Agumon and Gabumon)
More Appmons (Dokamon's line and Karan Eri)
New cards for Violet's deck in Liberator

My bets on the SECs are Hudiemon, a character whose mechanics are a spoiler like Kyoko, but not Erika since she's on the pack art; and GranDracmon, since he's postgame content like Sayo.

Other possible SECs that I'm not betting on: Arkadiamon Super Ultimate, since he's a new level 7; Eater Legion or Eater Eden, just to make the Eater deck less budget-friendly, and since Legion is also a character spoiler for Erika; Poseidomon, the associated level 6 Appmon; Violet's level 7; some other new bullshit from Liberator; Sistermon Noir; PileVolcamon