Yes, it's a brilliant idea, and as simple and evident as it can get.

But it is hack, though. Ideally, such functionality should be provided by WordPress already, following the "single interface for everything" mantra assigned to Gutenberg.

I experimented with adding settings for my plugin through Gutenberg. It is also an evident idea, since Gutenberg handles saving block attributes to the DB, and it makes it easier to implement many types of inputs (date/time picker, location, etc) which are not straightforward to provide using the standard add_settings_field function.

But, unfortunately, it doesn't really work, because relying on a CPT delivers a weird user experience: the document tab panel sidebar on the right does not make sense and it gets on the way, the "publish" button does not make any sense, the title and permalinks make no sense (even though they can be removed), and the idea that settings are stored as custom posts does not make any sense (all settings are already predefined, so I'd have to create a custom post for each of them in advance, and forbid users to delete them).

Being decoupled from the post editor, Gutenberg should be much more useful. I'm eager to see if, when the full site editor is ready and beyond, it will be possible to use blocks in entities other than posts (such as settings, dashboard widgets, users, media editor, etc)