After years of rumors, Eagle Gryphon Games finally announced that they will soon open the pre-orders for new contents related to Defenders of the Realm.
(image from Eagle Gryphon Games vlog)
In this new expansion, Companions & Catacombs, you'll be able to recruit companions and explore catacombs. There will also be an updated board for the core game, and another new expansion, The Hero's Calling, to design custom heroes for the game (and curiously not listed as soloable).