To expect that the Perl developers care for and maintain a module that you consider good is expecting a bit too much. CPAN is available and as you already understand, recommendations change. Hence this is why the Perl core aims to only include what is needed for/by Perl itself.
While agreeing with the lean core principle, I've seen Perl get severely eclipsed TWICE by completely inferior languages that sell themselves as a "kitchen sink" and as having "batteries included". This is about what people want and what Perl needs, not my favorite modules.
Clearly Perl is incomplete without modules or the corelist would not have over 600 items. The only question is what to include. My suggestions fall into 3 broad categories:
1. Complete Perl by bundling missing features (like a REPL)*
2. Update old interfaces and make things easier (like IO and Rule)
3. Encourage Perl use by using other languages in Perl! (FFI, Inline)
I would settle for Path::Tiny but this example from IO::All says it all:
* Frankly I would go wild with things like PPI, Perl::Tidy, Perl::Critic, Perl::Examples, something like Classic::Perl (expanded, for complete backcompat), B::Keywords, B::C, B::CC, Modern::Perl, etc.
open STUFF, '<', './mystuff'
or die "Can't open './mystuff' for input:\n$!";
my $stuff = <STUFF>;
my $stuff < io './mystuff';