I was actually thinking of something more Bricks-y than using files, although that would work too. I think it would be easier to use the Bricks template builder template types. Seen here:
Just add template types for Gutenberg only.
On further thought, perhaps an even better solution is just to add a drop down to template conditions that allows you to decide if the condition applies only to Bricks content, only to Gutenberg, or to both. The dropdown could be below the exclude tickbox.
