I just built Camer Pro, a theme for Blogging Theme Styles, which has full Gutenberg support. Although the default blocks are styled within the theme, the idea of plugins to enhance/add further blocks is probably something we will start to see theme and plugin shops develop as time moves on.

As this article points out, already has started, and I know Array Themes with their Atomic Blocks was one of the first I seen come out.

I think it's only a matter of time as themes start to add Gutenberg support at least, but plugin options will grow into a new market.