As always, what does "in Debian" mean?
In Debian Stable (i.e. 4.0, Etch) it won't ever go in - but don't
worry, neither will CPANPLUS.
In our development branches (unstable, testing), it will probably
enter shortly after its release - How long? Depends on its
complexity. Perl is maintained by Brendan O'Dea, not by our group, so
I don't want to put any words in his mouth.
Of course, I expect introducing a new major version will not be
hassle-free - so maybe the best way out is to start working on getting
CPANPLUS rolling as an independent package, which can later disappear.