Our themes will be impacted by Gutenberg as much as any other theme in the repository.
Normally, the themes are simply responsible for displaying the content as WordPress itself delivers it (this is true at least for the repository themes which are not allowed to include any kind of plugin-like functionality).
Gutenberg will replace/take over the editing part of the content, and anything that Gutenberg will have to apply/filter on that content will happen before the theme gets to display it.
There’s also the Classic Editor plugin which you can use to delay the Gutenberg switch (which based on the reviews is not quite welcome at this time).