Link: http://trac.tools.ietf.org/wg/httpbis/trac/ticket/34
Origin: http://www.w3.org/mid/2B319A4E-B0FD-4DA1-8B96-631B259A4F01@yahoo-inc.com
Component: p1-messaging
RFC2616 refers to RFC2396, RFC1630, RFC1738, and RFC1808, all of which have been obsoleted by RFC3986.
If the reference is changed, it will important to remember to make a decision about the "mark" production in the former (which are unreserved characters) which have been moved to have reserved status in the latter.
By referencing 2396, HTTP allows these characters unescaped in path segments, etc. If 3986 is referenced as-is, they will be effectively disallowed, thereby effectively making a number of existing HTTP URIs invalid.
This includes the exclamation mark ("!"), asterisk ("*"), single-quote ("'"), and open and close parentheses ("(" and ")").
RFC3986 is the standard based on full knowledge of its effect on HTTP. IOW, the decision has already been made.