This day was bound to come anyway. What was modern in 2009 for the Perl 5.10 era won't be modern soon.
I don't mind if you write
use Modern::Perl; and get the most modern semantics of the version you have installed. (I'm tempted to check if the distribution is more than two years out of date and print a single warning that Perl 5 has marched on, but you may be able to talk me out of that.)
I think the best option for the module is to recommend the use of a date, as in:
use Modern::Perl 2010; # Perl 5.12 semantics use Modern::Perl 2009; # Perl 5.10 semantics + autodie use Modern::Perl 2011; # Perl 5.14 semantics
This helps document the intent of the code, as well as the degree of modernity (or decrepitude) of existing code which uses this metapragma.
I know how to implement this. What do you think of the interface?