According to Tiny’s support window announcement, support and fixes for v4 have officially ended.
Today [Oct 10, 2019] we are announcing the end of support for TinyMCE version 4.x. It will be officially supported through to December 31, 2020.
TinyMCE was last updated in WP 4.8 to version 4.6.2. Since then, TinyMCE 4.x has had 37 releases.
Additionally, released in Feb 2019, TinyMCE 5.0.0 has had 39 releases (not counting any of the previews, betas, or RCs.)
We’re already way behind. The concern here is that this will be the next “support for dead PHP versions” that kicks along for 10 years without being addressed. Note that this petition isn’t geared toward “adding new features” to ClassicPress – it’s more about “avoiding technical debt” that becomes more and more difficult to shed later. Possibly, upgrading the editor might further solidify ClassicPress’ commitment to using a traditional editor.
A research repo may provide a path forward.
Will you be able to help with the implementation?
Yes, although it will be a few months down the road.