Late to the party, as usual, I picked Gladius - Relics of War on a Steam sale, along with the Tyranid and Chaos Space Marines DLC factions, expanding the original four faction options.
I dunno if these DLC factions have been patched in as available to be encountered in single player for those who don’t own the DLC, but I’ve encountered both of them as NPC opponents in my initial game this weekend. 
