At YAPC::NA this morning, chromatic answered my question about Modern::Perl, “What happens when perl 5.12 comes out?”, with what I think is a good solution.
The proposed answer is for Modern::Perl to take a date parameter to indicate what “modern” means. This is brilliant because it explains to even the unknowledgeable programmer when the code was current. Say the syntax is like:
use Modern::Perl as_of => '2009-06-23';
What could be more clear?