I think a Lua plugin was mentioned somewhere before. Really, I think Lua is the best bet when it comes to integrating a scripting language. It’s familiar to many and is very mature and well-performing.
Though to be honest, I don’t see the point. Epic decided to abandon UnrealScript, which was tailor-made for this engine, in favor of full C++. They did it for a very good reason after years of experience with UnrealScript.
I feel like people trying to reverse that decision in one way or another are going to encounter the same issues Epic did.
Do you say this from experience with Unreal? I can’t necessarily agree, because I don’t see how it would be much different from the C++ experience.
Epic has gone to great lengths to ensure the C++ experience in Unreal is smooth. The header tool takes care of all the metadata building, while the engine’s standard library provides all of the tools you’d need to create what you want. Hot reloading is an amazing convenience.
I really can’t see anything significant C# would offer that C++ and Blueprints don’t. I do see though that it would introduce another language that would need to be supported which is a tremendous amount of work. A language that at first would not have any kind of integrated debugger like C++ or Blueprints. It would introduce another way to do something that isn’t all that different from C++ (I don’t think thats a good thing). Without CLR modifications you would not be able to use hot reloading with C# because the CLR does not allow such a thing. You might have less issue with interop if it only uses the Blueprint API, but I have little doubt people will begin asking/demanding for more stuff to be exposed to C# instead of using C++.
I say this as someone who has used both C++ and C# for years and is rather experienced with both.