If they don't enforce their trademark they'll lose it, so as depressing as it is my prediction is that they won't allow it. Even though there's likely little value left in it for them.
Enforcement doesn’t mean they can’t allow the community to use it under clear guidelines. Or if they’re not using it any longer commercially, O’Reilly could transfer any rights they have to the Perl folks and they could allow O’Reilly to use it for its back catalog or whatever.