CKEditor 5 is a completely different editor to CKEditor 4. The plugin model that exists currently, as far as I can tell, is just not possible. It’s more a case of “replacing” than “upgrading”. But CKEditor 4 is still supported until 2023. I had a session at Collabsphere on the complications in the current landscape with web rich text editors. quill-better-table is okay for a basic table, but from what I saw it suffers from the same (or worse) limitations for more advanced table functionality, e.g. bullets/numbering in a table and tables in tables. I think providing table support could lead to end users expecting a level of functionality that is not available. At least it’s easier to get HTML out than some of the newer breed rich text editors / frameworks.

Quill is a nice simple editor and one of many I looked at earlier this year. But it’s important to be aware of its limitations and for that reason I wouldn’t recommend it for existing content or content that needs to be edited in Notes Client. Tables are particularly problematic. Formatted pasting of HTML content may also be a challenge - I didn’t investigate in enough detail to try that.