Celestial heavens interview in April asked the question and got this answer.
CH: M&M fans love modding. Will this be possible? What can you tell us about it?
Answer: Alright, about modding: We plan to release an editor for Might & Magic X. On top modders will get access to almost everything in the game from level building, adding objects, changing textures, adding monsters, modifying values, creating texts, etc.
Will it be super easy? No. Why? It's a tool, it takes time and it takes dedication. It's 90% the same tools we are using to create the game right now. We are optimizing to make it as accessible as we can but it's not a "one-button-create-fun" solution. Nevertheless, we are confident that we will see user created content for Legacy.We'll talk about and introduce to you this particular topic in more details later during the development.
In fact all these interviews look promising in many ways: