Cool. My only nit with it (and it's a nano-nit) is that $pkg is being passed as an arg to export_to_level, which gives the mistaken impression that it means something, when in fact that argument is ignored. Do you happen to know of plans to make that argument actually meaningful in the not-too-distant future? If not, I'd make that line

  __PACKAGE__->export_to_level($level, undef, @EXPORT)
    if $pkg;
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