My gut feeling is to agree with toonburner. There are old caches which many of our community enjoy looking out for and then finding. Some of these are in out-of-the-way locations. Having a cut-off date can be left until later in the discussions. There is only 1 real question - to preserve or not to preserve. I always feel it is sad to see a cache I have searched for and found disappear from the list. I agree that owners should have the opportunity to archive caches that they own but any that are disowned in any way should be allowed to be adopted by the community.
I vote Preserve.