Alt-Svc across a domain?

Howdy,

It is common for web sites to serve content from a variety of different
origins within the same domain. For example, www.example.com,
accounts.example.com, images.example.com. A single page view may require
loading resources from several such origins. (Tricks like domain sharing
can exacerbate this proliferation of origins.) It would be great if the
service had some way to tell the client, "All of my domains can use this
alternative service". What would folks thinks of an include-subdomains
parameter in the Alt-Svc value? If such a parameter were present in an
Alt-Svc advertisement, a client could use this advertisement to apply to
any sub-domain of the origin that the client does not already have an
alternative for. This would avoid the need to discover the alternatives
individually.

Cheers,

Ryan