Not sure if this is something I would ever be capable of doing myself. I was thinking, since Unity is an engine running on C/C++ using C# to communicate with the built in functions/ API (My personal understanding), maybe it would be possible, without too much effort, to convert it to Unity, or atleast the skeleton, template. Maybe with the new Entety system it would be interesting for you aswell. My programming experience is limmited to C# in Unity. No Idea how to build an engine. Maybe I should look into it