UNIVERSAL.pm itself is not so important. It's mostly just documentation. The guts of the UNIVERSAL package (UNIVERSAL::can, UNIVERSAL::isa, UNIVERSAL::DOES) are hard-coded into Perl, not part of a module.

The disadvantage of having UNIVERSAL::new is that all packages automatically inherit from UNIVERSAL; even ones not designed to be used as classes. How much sense do things like this make?

use strict;
my $thing = strict->new;
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A whole lot of modules would need to add code like this to them:

sub new {  # override UNIVERSAL::new
  require Carp;
  Carp::croak("$_[0] is not a class");
}
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