Personally I do not usually list core dependencies.

Modules can be removed from core, which will technically break your distribution if you haven't listed them as dependencies. However, for people who have problems installing your distribution, the fix is simple (and quite obvious given the error messages they are likely to see) - they just need to install the dependency first, and then install your distribution.

Besides which, the deprecation cycle for core modules is quite long. If, after releasing Perl 5.20, p5p decide to drop module Foo, then Perl 5.22 (released a whole year after 5.20) will need to include a version of Foo that issues deprecation warnings, and 5.24 (released a year later again) will be the first version without Foo.

So if you pay attention to what modules are being discussed, you'll get maybe 2 years' notice about module removals. Plenty of time to push out an updated release listing an extra dependency. (And if you don't have the tuits to upload a small bugfix update in 2 years, you should probably think about taking on a co-maintainer.)

Even if you pay no attention to what's going on in p5p, you'll start seeing lots of test failures from CPAN smoke testers on the Perl 5.23 development releases many months before the Perl 5.24 release date.

There are some modules that seem unlikely to be removed in the foreseeable future - strict, warnings, constant, overload, Carp, Exporter, Scalar::Util and Test::More for example.

So why don't I list them? Seeing a long list of dependencies can put some people off using a module. Type-Tiny says Dependencies: none, just as a "::Tiny" module should. :-)

However, Type-Tiny does list a "test_requires" dependency on Test::More 0.96 in META.yml. Why? Because I need 0.96 or above. Perl 5.8.1 (the oldest Perl supported by Type-Tiny) ships with Test::More 0.47. The first Perl to ship with Test::More 0.96 in core was Perl 5.13.4. So that's a reason to list particular core modules as dependencies - you need a newer version than what was bundled with some of your supported versions of Perl.