When I was thinking about this problem a couple of years ago (eek, time flies!) I came to the conclusion that the only archival approach that was viable for thi

When I was thinking about this problem a couple of years ago (eek, time flies!) I came to the conclusion that the only archival approach that was viable for this was to have a dedicated url resolver service that was independent of the DNS system and could be swapped out. Obviously you wind up with resolver resolver resolver services if this goes on for too long, but it is one of the few workarounds for the fact that time (and many other things) are not reified in the DNS system.