For the past couple of years, we have been hearing about how hard it is to break into the WordPress theme and plugin markets. I think there will be a large shakeup with WordPress 5.0. Plugins especially will have to scramble to be compatible and take advantage of Gutenberg. Some will be slow with updates, which will open the door for new players. Also, I expect that we will start to see some very creative and useful blocks. We will probably have too many blocks to choose from … but some will provide compelling and feature rich options that capture the market.
The WP plugin repo is already being flooded with plugins that provide special blocks such as pricing tables, galleries, contact forms, portfolios, etc.
The editor template options will be interesting. I imagine a template editor that will allow you to create templates for Custom Post Types. Speaking of Custom Post Types, if you have the blocks in the Post and Page editors, then there may be cases where a CPT isn’t needed anymore. Of course, they help for organizing your content, but they won’t be needed if you were just using them for some extra feature that could now be a block.
If I owned a theme shop, I would create a React WP theme and provide blocks for the header logo, menu, etc. and a layout editor. Then let users create their templates using Gutenberg.