sorry I haven't had the time to comment on this 'til now...

this implementation won't work in some cases. take, for example: youtube.com and youtu.be -- both should use the same sitemodule, but this implementation would require 2 separate sitemodules. That's why I didn't end up doing it this way in betterzoom.

it's a stylistic preference, of course, but I'm not entirely in love with having a sitemodule called "youtu" that is just an alias to the youtube one.  Mostly I'm thinking about coming back to it 6 months later and scrolling around -- in betterzoom, there's a "domains" list that works similarly, but essentially auto generates the mapping of domain to sitemodule.

I think I'd prefer we modify and go that route for readability. I think it's nicer to look at the sitemodule that handles "youtube stuff" and see a list of domains it applies to instead of having to search for a sort of "domain fragment"... thoughts @andytuba ?