The first answer is Perl 6 - it will come with a strong object system in which much can be declared, so I guess it'll make most (or all) of Moose and MooseX::Declare superfluous.

But I agree that Perl distributions are a good idea. Actually ActiveState ships with more than just the core modules by default, and I wouldn't be surprised if Strawberry did as well. Many Linux distributions already have native packages for many CPAN modules (for example Debian has packages for Moose, named libmoose-perl). So it's already happening in some sense.

Putting more modules into the Perl core is to be avoided, and neither the Moose folks nor p5p really want it.