Shades of Darkness - Discussion

Hello! I wanted to ask about a pressing question. My friend and I play together, and I would like to get this, shall we say, expansion pack, but my friend doesn't feel the same way about the Dungeon and doesn't see any point in buying it. So, here's the question: is it known whether there will be compatibility between the regular Heroes 6 and "Shades of Darkness"? Will we be able to continue playing together, or will we both have to buy the expansion pack to play?