Nice - I think we will make the switch to this. We wrote a Common Lisp kernel for Clasp (Common Lisp system that interoperates with C++ and uses LLVM as the backend -https://github.com/clasp-developers/clasp) We implemented ipykernel and ipywidgets in Common Lisp by translating the Python code. I think we could switch to Xeus and lower the maintenance burden and contribute to Xeus.