Horus Heresy is still done by the Specialist Game team, who also work on all the other Specialist Games: TOW, Middle-earth, Legion Imperialis, Necromunda and Bloodbowl.
Right now the majority of TK and Bretonnia are out of stock, and we know both have more kits to be released (Foot Knights, Green Knight, mounted prophetess, Casket of Souls, Bone Giant, Carrion). It's safe to assume the remaining factions will receive a similar amount of attention that TK/Brets did.
Can they get all nine out this year, with their current stock/production issues? I think a roadmap will put that question to rest.