Pinto in Perl

Just checked out the latest episode of FLOSS Weekly about an application named Pinto In short, you download Pinto from CPAN and then run some commands to tell Pinto what Perl modules you are using and it will download the modules and keep track of them.

A couple features discussed on the show:

• ability to create different "stacks" of Perl modules for different environments (development, test, production, etc) or operating systems (Windows, Mac, Linux) 
• Version control of your stacks
• "Pinning" which is locking a module to a specific version
• Ability to merge in local modules that you don't want to be available on CPAN

After hearing a description of this, it got me wondering why these kind of things aren't available in CPAN in general? The main reason I can think of for not doing this is that it would vastly complicate the current CPAN set up.

If anyone pins an older version of a module, CPAN would have to keep that available forever. It could also lead to complexity tracking what is a local module not available anywhere else and what is a module available in CPAN in general.