With version 1.5+ Gutenberg is finally in a state where it is usable for the first time: with added Meta Box support and other refinements. I am pleased the Gutenberg team has listened to at least some users who gave feedback. Please keep on that route! :-)

I would still prefer and recommend to use as a plugin first for at least 6 more months. This thing is so huge, it just needs more time. The worst thing would be to ship it as alpha/beta software to millions of users and the reputation of WordPress goes down the hill... No one could want that to happen.

Otherwise, now for the first time really the full potential Gutenberg has shined on us a little bit more with 1.5+. Imaging "templates" or Themes just built for Gutenberg will bring a whole new chapter for WordPress. This all makes a lot of sense very soon.

But please always remind: don't force anything on users which is not ready for prime time. Just give this thing more time - the better the "product" will be and much more of a success in the end.