I discovered the %_ variable when I tried to write

sub foo {  # takes a hash argument
  my %_ = @_;
}
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and discovered that that doesn't work. Later, I thought "of course" (because of typeglobs!) and used local %_ instead. Although the presence of "the same" %_ regardless of package may be a problem, as mentioned above, maintaining this should be no more difficult than similar code using $_ and @_.