Context

Currently, the plan is for the next major version of the Jupyter Notebook to use JupyterLab components. However,many people are still using and developing on the v6 notebook setup. This is particularly challenging for people buildingextensions that depend on APIs that will soon be removed. For example, I recently found out that a large university started building a custom grading UI on top of the v6 notebook UI, because they didn't realize it was going to be switched to JupyterLab.

Proposal

I suggest that we add a large‼️ DEPRECATION to any of the current documentation pages that discuss extension APIs that will be deprecated. For example,the front-end interface page. We can then include a link to the Jupyter Notebook v7 plan and help clarify confusion before people are surprised.