The following utilities will be removed from the core distribution in a future release...
I think this is the first notice that, maybe in 5.20 or later, CPANPLUS and the associated tools will be removed. 5.18-RC2 certainly includes cpanp, as I've used it to test installation of modules.
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.