Perl update to 5.22 in current arch (~) as well as various per-core/* dev-per/* and corresponding virtual/perl-* happened in Funtoo portage tree and gave a various problems:
1. 5.22 version has incompatible changes with older releases for example:
Error: Can't use 'defined(@array)' (Maybe you should just omit the defined()?)
2. This breaks (or makes misfunction) of quite a lot of packages, to name a few:
dev-util/intltool important core package
www-apache/mod_perl segfaults, hence no Apache work possible.
sys-devel/autoconf autoscan tests fails with perl-5.22
sys-kernel/openvz-rhel6-stable failing with perl-5.22 due to above mentioned "defined" problem. A blocker in deploying openvz boxes.
That's only a few problems I faced myself, so there're could be many more.
Likely it just didn't tested in gentoo-x86 or did not test completely.
3. stable dev-lang/perl, perl-core/, dev-perl/ and their virtuals versions are known to not causing lot of problems.

Possible solutions:
1. perl freeze. maybe not a best things because we have a borken state in ~arch
2. Fork of all perl framework (perl itself, perl-core, dev-perl and virtuals). This is also a rough tasks.
3. modification of merge script to have ability to scan all of perl core packages keywords and merge only stable versions. This will cause massive downgrade on ~arch and this require: tests (it could run smooth or not), explanation and News item on how to deal with it. This brings back stability in packages. Personally, i favor this one.
4. run massive QA builds to hunt all of possible perl-related breaks and report: this is has no time limits of getting all things fixed in near days, weeks, etc.