In reply to Justin Tadlock.

As I mentioned above, having this feature included in the Classic Editor plugin wouldn't stop you from doing this. With a simple option for selecting the "Default editor for all Widgets", next to the other existing options, would allow you keep using Gutenberg while also disabling Gutenberg for the Widgets screen. I think it makes sense to keep like functionality (i.e. disabling of Gutenberg) all in the one plugin. It certainly helps end users, in particular those millions of users that are already using the Classic Editor plugin.