@benh: I was thinking about similar issues, but from a different point of view: Currently links to documentation of other parts seems to be mostly done with links to other documentation pages, which kind of hard-codes the layout of the generated documentation, and makes it hard to extract links for other documentation browsers (command line interfaces, desktop documentation browsers, or extracting related resources).
My idea would’ve been to have a rust scheme for links, like rust://crate/mod/type.method or rust:/mod/type.method for local references. Though the crate part is a bit hard to do if you want to reference non-dependencies, since you’d have to resolve it somehow.