> For historic reasons,

Sorry, which historic reasons?

If you don't like caller's interface - where I sympathize - I'd rather propose something more flexible like returning a hashref:

   DB<116> sub __CALLER__ { 
           my $level = shift;
           my %hash; 
           @hash{qw/package filename line subroutine hasargs wantarray
+ evaltext is_require hints bitmask hinthash/} = caller($level+1); 
           return \%hash 
           }
  DB<130> sub tst { print __CALLER__->{subroutine} }

  DB<131> tst()
main::tst
[download]

or

  DB<136> use Data::Dump qw/dd/

  DB<137> sub tst { dd __CALLER__ }

  DB<138> tst()
{
  bitmask     => "\0\0\0\0\0\0\0\0\0\0\0\0",
  evaltext    => undef,
  filename    => "(eval 108)[multi_perl5db.pl:644]",
  hasargs     => 1,
  hinthash    => undef,
  hints       => 256,
  is_require  => undef,
  line        => 2,
  "package"   => "main",
  subroutine  => "main::tst",
  "wantarray" => 1,
}
[download]

Though not sure about using this underscore __NAMESPACE__...

And I'm pretty sure about reinventing the wheel ...

... CPAN is so big and I'm so lazy ;-)