Fallback flow for /site-meta for top level domains

(sorry for potential duplicates, I'm having problems posting to the list)

This issue was brought up by Google.

There are many cases where the HTTP server for example.com resides at
www.example.com. Should /site-meta specify that if a top level domain
returns a 404 for a GET /site-meta, the user-agent must try the same request
for www.*?

EHL