Testing individual plugins is only going to help so much. Sites use a variety of plugins which interact with each other. Then there are premium versions of plugins, plugins bought from developers and not available on the WordPress plugin database. Also, old plugins and plugins not updated on user sites.

I've been working to eliminate plugin use on my sites. I've gone back to simple posts using standard HTML, no extra code from plugins. My sites should be fine with whatever changes roll out in WP 5. If not I have already looked at other options within WP and alternative CMS.

The interesting part of Gutenberg and plugins will be all those page builder plugins. Will they merge with Gutenberg or become obsolete?