Currently the notebook API consist of three parts: content persistence (content provider), notebook execution (notebook kernels) and output rendering (output renderers). This abstraction can help reduce redundant code, for example, .NET and Python Jupyter notebooks can share the same content provider as the parsing/persisting logic is identical.

However, it's not clear yet how language extensions would opt-in if the content provider is shared. One example is how would a .NET extension decide if it should contribute actions/commands to the editor title bar / context menu in a ipynb files.