I open this issue following #8503 (comment) to keep track of the missing features or anything that could be improved.

Feature status

• Test integration with Google Colab following Using raw.plot in JupyterLab or Colab #8080 (comment)
• HiDPI rendering of 3D and mpl widget (see MRG, ENH: Add a screenshot button to the notebook 3d backend #8708 (comment))
• Screenshot w/time_viewer is off in the vertical direction (https://github.com/mne-tools/mne-python/pull/8708/files/5d34669c5ea051b1c08dfda19cb1ddf0ba727945#diff-a6e2fc2fab82c1377cb29516fc0a7aed813ee4273daad18cf002e7302a331770)
• Update to ipyvtklink (Rename to ipyvtklink Kitware/ipyvtklink#30, MNT: Migrate to ipyvtklink #9341)
• Button/shortcut for autoplay (ENH: Add a playback button to the notebook 3d backend #8741)
• Button/shortcut to take a screenshot (MRG, ENH: Add a screenshot button to the notebook 3d backend #8708)
• Button/shortcut to save a movie (ENH: button to save movie #9190)
• Button/shortcut to display help (ENH: Help button #9123)
• Label time course mode (MNT: notebook conditionals in Brain & _update #9016)

Design/UX

• big square button (asked in MRG: Prototype of notebook viz (ipyvtk) #8503 (comment))

Known issues

JupyterLab

• matplotlib is not interactive Javascript Error: IPython is not defined
• The mesh is translucent
• A VTK window opens on local instance

Google Colab

• It is not supported yet (asked in MRG: Prototype of notebook viz (ipyvtk) #8503 (comment), standby in ENH: Notebook 3d backend improvements (ipyvtklink) #8704 (comment))

A testing notebook is available on gist.github.com.