would it be possible to add support for other languages for plugins development?
Sure. Infact it is already possible and no harder or easier than writing them in C/C++.
The requirements for plugins:
a) They need to be a shared library (dll)
They need to export a few functions in a C-style interface
int beginPlugin(HINSTANCE hDllInstance);void endPlugin(HINSTANCE hDllInstance);LPCSTR pluginInfo(int field);
and that's all.
The magically tight integration with blackbox of course comes through using bblib and sending/receiving bro@ms for which a wrapper in your language of choice would be convenient, but not required (as long as you can import/call C-style functions).
For C# it is surprisingly straightforward, but meeting these requirements is a little tricky for other languages which bring their own runtime like Python, Lua or Java.
For those you will need a wrapper binary in one form or another. (In java you can at least use JNA to access bblib)