I would like to share my experiences and test with GP and Gutenberg. I think that above all Themes and Gutenberg will have a future, while pagebuilders have to dress warmly.
I like to use Gutenberg very much because I just have to use the editor directly and have an enormous flexibility to design my contribution. The danger? The design is not uniform. I would like to give an example: I use the newest block from Gberg (http://prntscr.com/laf66u) but this creates an imbalance to other blocks (no fixed padding to the headline and no uniform font to the headlines). In comparison the example of the button: http://prntscr.com/laf76o (padding: 11px 24px;)
What I mean is: I would like to have a theme that allows me to define a uniform design in one place without having to screw in a hundred places.
I know that GP and Gberg are in their infancy, but maybe you can include that in the roadmap.
And as always: additional blocks (Accordion, Alert or even a Table of Contents block would be very fancy.)
I (and i think others too) would be very happy about that.