HTML email is a bear, even with templated services like MailChimp. For that reason Civimail will not be compatible with Gutenberg. Why? Because most HTML5 editors are not compatible with email-style HTML. In order to ensure that an HTML email looks pretty much the same for all users across platforms, you end up having to use old-school borderless tables with styles embedded in the HTML. Style sheets and divs simply don't translate to email because html mail protocol is still over a decade behind browser html technology. Develop a simple html mail template with borderless tables and embedded styles. Make the template a fixed width of 500px. Even more critical is whether the email has images embedded or stored on your site, but that's beyond the scope of this response.
Frankly, younger users eschew email altogether at this point. You're better off creating a short text, twitter or instagram post with links to a news or newsletter post on your WP site. Of course your post on the WP site itself would be Gutenberg friendly.
Edit: Of course you could also go with an extension like CiviCRM Mosaico as Fabian suggested above. ;)