[Where] do I plea for it to be included in the core?? :-)

You don't. That's the surest path to stagnation and ossification. The module would then have to be backwards compatible until the implosion of Perl 5, and I'm not interested in that.

When this pulls in other modules such as signatures and Method::Signatures, it'll have non-core dependencies that prevent it from being considered for core, and that's fine too.

But that is kind of my point. See, foreach version of perl >= 5.12, we should have a modern.pm pragma that will croak unless you have some (modern) CPAN modules installed and at the same time, and it will enable the most-modern things perl+CPAN have to offer at the time.

This way,

use modern
[download]

in 5.10 would enable strict/warnings/say/given/err etc, in 5.12 it will enable _that_ and maybe signatures, mro 'c3', in 5.14 ... you get my drift.
[]s, HTH, Massa (κς,πμ,πλ)

The consensus on p5p seems to be that it's more important for old programs to run unmodified on modern versions of Perl than for modern features of Perl to be available by default. In theory, use 5.10; would enable all of these features for 5.10 programs and use 5.12; for 5.12 programs, but the feature pragma at the heart of that behavior does not enable strict and warnings, and the version number keeps changing as what's "modern" changes.