All teams in the LRB will be in the Legendary Edition.
Kislev is a reskin of Slann, a team that was never officially released by GW but is widely played on table top due to being one of the three new teams in the LRB (living rule book). Other pseudo official new teams (Chaos pact and Underworld) used existing players, but Slann was all new players/race and for some reason that means they’d rather reskin them. Underworld will be in as-is, while Chaos Pact might or might not be in (I’m unsure on this). So Chaos Pact might be the only team missing.
Note that the Slann were canon in Warhammer, so I’m unsure why the reticence to bring them to Blood Bowl.