The thing that really concerns me with WordPress and Gutenberg is performance. Gutenberg is great but there is never much concern to making the front-end less top heavy. Gutenberg is likely to make this worse. Each block will add it's own CSS and JS...and the bloat will be immense. Instead of users adding a single page builder plugin, they'll add a whole bunch of individual blocks and each one will load more and more external scripts. PageSpeed scores will be dismal.