[justinator]

>assume a single version of dependencies will be installed on any system which causes untold nightmares when it turns out that there’s a non-backwards compatible update to something three dependencies deep that you weren’t even aware you were using.

I may not completely understand what you're describing, but with perlbrew managing different Perl versions, and various CPAN clients installing modules in versioned libraries - as well as the test/smoke servers that test CPAN on tons of versions of Perl for Perl CPAN authors automatically, I don't know if I've come across what you're describing.

What's still a pita is when there's an outside dependency from the Perl ecosystem that breaks a module, but I'm not sure that's Perl's fault.

[dhosek]

It happens more with CTAN where there is no possibility of a testing framework and there is no ability for multiple versions of an artifact to coexist.