I, for one, would like to see the IETF host an public archive
of expired I-Ds for technical reasons. Having past works, even
those not worthy of RFC publication (on any track), available
adds to wealth of knowledge available to future Internet
engineering. This will allow future efforts to take full
advantage of past efforts. Having them available for IPR reasons,
IMO, is secondary (as it addresses a non-technical issue).
I suggest that the URIs for an expired I-D contain the word
"expired" to limit confusion with active I-Ds, e.g.:
http://www.ietf.org/EXPIRED-INTERNET-DRAFT/draft-....txt
Kurt