The Creation engine by Bethesda is still highly mod friendly. For example, there is a fan-made total conversion mod being created for TES V: Skyrim that is a remake of TES III: Morrowind [1]. Also, the SureAI team is creating Enderal, a total conversion mod in a completely different setting [2].
https://www.youtube.com/watch?v=X173LZkEgYc