Is the simple reason that none of the following relative (i.e. not absolute-URI) autolinks are supposed to be working, that it is too hard to distinguish them from HTML tags?
<directory/> <file.ext> </root/file.ext> <./local/file.ext> <../upper-level/file.ext> <#target> <?query>
Link titles are not explicitly supported in autolinks. Was that a deliberate decision, especially since internal whitespace is disallowed?
<long file.ext> <email@example.com "My Name"> <http://example.com "standardized example domain">