Notebook import converter

I am the author of Cadabra (, a symbolic computer algebra system which has its own (native, non-web based) notebook interface. There is a Jupyter kernel for this system too, so that it can also be used that way. However, the notebook file format is (for historical reasons) not .ipynb.

Is it possible to write a JupyterLab extension which enables users to auto-convert Cadabra notebooks, so that users do not have to run a separate tool to do this, but can simply open a Cadabra notebook and have it convert on-the-fly to a Jupyter notebook? I will write the conversion step; the question is purely about the possibility of hooking it into JupyterLab as described above. Any pointers are welcome. Thanks!