(I really struggle to make sense of JupyterLab extension code and dev environments were any fixes required; the activation energy to try to even get started is just way too expensive for me right now:-(
Did you ever get anywhere with an extension to style notebook cells based on cell tags in a JupyterLab or RetroLab UI? The lack of such a feature continues to be one of the blockers to me moving to JupyterLab for teaching and learning purposes, where we make heavy use of extension styled notebooks based on tag attributes.
sorry for the super late answer to your question, which did not hit my radar at the time:
The answer is no; I’m on exactly the same page as you seem to be, in that a) there are many things that draw me back to the classic notebook even though I know the whole community is pushing towards jlab, and b) I feel totally overwhelmed when it comes to jlab extensions