I been reading through this, and this sounds like the kind of stuff I do on a daily basis. Qt is normally written in QML, but I usually write it in C++. C# is a good programming language to use for its cleaner code but it can't really port for different OS. I haven't really written any game engines but I've made some applications before. If you guys want to use C# I'd suggest using DirectX 3D11 as a base and test it using OpenGL and have some option for the end-user to pick which render mode would be best.
Ruby is worst scripting language in existence. Also the occulus rift thing is overrated.