Some thoughts from a Perl perspective (which wasn't mentioned)

• companies could restrict their proprietary modules to the same top-namespace like Apple::
• build systems could refuse to install from such private namespaces
• examples like My:: or Our:: come into mind as private by default
• CPAN could deny releases into "private namespaces" or similar
• another option for privacy could be leading underscores package _CompanyModule;

Disclaimer: I didn't thoroughly check if any of this is already done. But I found at least one module released under My::Object