Why not have the copyright fall over into a sub category where the copyright still exists and anyone who wants to use it pays, directly to the copyright office, a set License fee per unit based on a % of the wholesale price the item is sold for to use it for commercial use but allow unlicensed use for all non-commercial purposes?
A small % of the fee could then be used to fund the work involved to document the use and fees payed the rest can go to the copyright owner should one surface and the work could then revert back to a normal copyrighted work to continue until the original copyright was due to expire. Any fees not claimed within the copyright period could then be used exclusively to fund the maintenance of an electronic public domain repository.
Clearly it would have to be established what steps must be taken by a potential commerial entity to establish and contact the copyright owner and some burden could still be placed on the owner themselves. They need not be required to register the copyright but if they don't register it within 5 years of the work's creation and the work becomes considered abandon because they didn't register and couldn't be contacted then they must accept the set fee rather than be able to sue for breach of copyright as long as the commercial entity which used the work can show they followed the steps required to attempt to contact the copyright owner.
Someone smarter than me will surely point out some flaws in my thinking but I am sure a workable solution based around these ideas could be implemented.
