Why not use Python or C# then? All the engine-apis are custom anyway: it just comes down to different containers, datatypes and new syntax to learn. Why reinvent the wheel with a new language.
This will be another one of these niche languages that can never compete with widely adopted languages like Python/C# that have grown for years on a much larger userbase.
The heavy stuff has to stay C++ anyway for performance reasons. Why not build a lightweight python wrapper that is easy enough to use for level-designers/artists and under the hood interacts with the c++ apis (so c++ documentation doesnt get completely abandoned). Much like Pytorch or Tensorflow