I think I just figured out two major things I wanted to work out:
Not sending the entire route config to the client, only the ones that matched and that are linked to on the page.
Defining routes manually in replace of, or in addition to, the conventional file-system routes
The reason I've been hesitant on (2) is because of (1). Take a highly interactive blog where each article is a full blown React component like our blog instead of just markdown you can lookup and parse on the server.