I don't know where the deprecation of CPANPLUS comes from, but I think it just hasn't seen much maintenance and carries quite some overhead in term of modules. Of course, CPANPLUS will stay available through the CPAN.

Hmm, I kind of think that info might be important/interesting

Nothing here or todo.pod, and I think I found it:) Taking CPANPLUS out of core - nntp.perl.org , [Round 2] Taking CPANPLUS out of core - nntp.perl.org and https://github.com/phaylon/perltodo/blob/master/CPANPLUS-Deprecation-Tree.mkdn, and How do we know when a CORE module is deprecated? | chris fedde [blogs.perl.org]

It appears somehow they've determined that "CPANPLUS did not replace CPAN.pm as the CPAN client of choice" so out of the core it goes :)

Along with the above, a reading of perlpolicy made it click for me :) I think a link to https://metacpan.org/module/RJBS/perl-5.18.0-RC2/pod/perlpolicy.pod#deprecated , one of

    L<perlpolicy>
    L<perlpolicy/Terminology>
    L<perlpolicy/deprecated>
[download]

for the perldelta deprecation section would be useful -- cross reference and all that :)