...a lot of us are practically addicted to Jupyter Notebook Extensions [1] features and these aren't compatibly with Jupyter Lab and Jupyter Lab didn't add equivalent builtin features.

Once you get used to little things like (a) auto-TOC/outline of current doc in a sidebar (with highlight for current running cells and other goodies), (b) auto scroll to end of output, (c) browser notifications for end of long running calculations (so you can be alerted of stuff being done while browsing in other tabs) etc. etc. you really can't live without them!

It's this little things that matter 100x more than freely rearrangeable tab-grids and detachable outputs and terminals... these are cool but it's the other small details that make a bigger difference in productivity!

(As someone who also has some frontend web experience I was planning to maybe try and code these and contribute, but I never find the time, and last time I looked I couldn't find a good entry point to start learning about jupyter lab's frontend code...)

[1] https://github.com/ipython-contrib/jupyter_contrib_nbextensi...