An object in Perl is most often implemented as a hash, because an object is key/value store of attributes and a namespace by which the compiler/interpreter can locate its methods. Even in Moose, they are still most often implemented as hashes, so you can always add "attributes" at run time, you just don't get the type checking, coercions and automatic attribute accessors.

package Class;
use Moose;

package main;
use strict;
use warnings;
use Data::Dumper;

my $obj = Class->new;
print Dumper $obj;
$obj->{foo} = 'bar';
print Dumper $obj;
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You have to ask yourself, why do i need to add attributes at runtime and if still valid, why do i need Moose sugar to make my code only slightly easier for me to churn out at the expense of reinventing Moose, as the "contentious solution" you linked to points out.

L-LL-L--L-LL-L--L-LL-L--
-R--R-RR-R--R-RR-R--R-RR
B--B--B--B--B--B--B--B--
H---H---H---H---H---H---
(the triplet paradiddle with high-hat)