Is there a template for JEPs? edit: Yes there is! https://github.com/jupyter/enhancement-proposals/blob/9a608e88be32af66757785b8e0f48541e71388a8/jupyter-enhancement-proposal-guidelines/jupyter-enhancement-proposal-guidelines.md
Otherwise I think I’d combine the first post of this thread and https://github.com/jupyter/nbformat/issues/148# to make a start.