Agreed. And this wouldn't have to wait for github to implement. Perhaps its possible to create a webservice that could examine the forks in a network graph to identify the most active fork -- and provide a url for the repository that resolves to this most active fork. Something like bestfork.com/reponame --> github.com/newmaintainer/reponame

EDIT to be more precise, my example github link should read github.com/defactomaintainer/reponame