Code that uses Modern:Perl will be more likely to break when Modern::Perl or perl is updated....

First, it's not for you. You're a Perl guru. You don't need it. You know how to twist and mold Perl to behave how you like through pragmas and modules.

Second, I'm likely to add a year flag, so that people can (optionally) request a specific-but-recent version of modernity.

Third, anyone who blindly upgrades code without testing it has bigger problems than a silly little module like this.