The Perl 5 porters officially ended support for Perl 5.8 on November 5, 2008. Fortunately, Enterprise Support exists to help your legacy Perl 5 installations cope. Distributions such as Red Hat Enterprise Linux and its offshoot CentOS will continue supporting old versions of Perl 5 for up to ten years since their release (the release of the distribution, not the release of the version of Perl 5 they distribute).
For example, the most recent CentOS release, CentOS 5.6, includes Perl 5.8.8. (CentOS 5.6 came out just over a month ago. Perl 5.8.8 is seven stable releases out of date.)
In seven years, when
CentOS 5.6RHEL 5 reaches the end of its supported life span, Perl 5.8.8 will have been unsupported by Perl 5 Porters for nine and a half years, and will be almost thirty five stable Perl 5 releases out of date.
But it's supported and it's enterprise, so the CPAN authors of 2018 must be sensitive to the needs of their users, and so the earliest you can rely on Perl 5.10 features such as
If Perl 5.16 gets a meta-object protocol and support for a stripped-down version of Moose as its default object system, CPAN authors can start using it in 2019.
If that doesn't make you want to fire up your favorite text editor and start making plans for all of the wonderful things you will eventually be able to do in the far future, consider also this. If the oldest supported version of Perl 5 is 5.8.8 (even if the people who wrote it and maintain it and support it have disclaimed any interest or desire or intent to support it), then every subsequent version of Perl 5 is a supported version of Perl 5. With Perl 5 on a well-tuned yearly release schedule, you can expect a new major release once a year and three or four point releases in that major release family every year. That is to say, Perl 5.12.0, 5.12.1, 5.12.2, and 5.12.3 are supported. Perl 5.16.0 through Perl 5.16.3 will be supported.
Because you as a CPAN author can't leave all of the people paying good money to CentOS to support Perl 5.8.8 for the next seven years out in the cold, you have a lot of free time not using new features or removing workarounds for Perl 5 bugs, and you can use that time to test your code on an ever-increasing number of supported releases of Perl 5 in the intervening years.
Fortunately, we have great tools such as App::perlbrew which can install multiple parallel versions of Perl 5 without conflicting with the system Perl 5 installation, so that you can install Perl 5.8.9, Perl 5.10.0, Perl 5.10.1, Perl 5.12.0, Perl 5.12.1, Perl 5.12.2, Perl 5.12.3, and (soon) Perl 5.14.0 on your CentOS 5.6 or RHEL 5.x system to test that your code will continue to run on every supported version of Perl 5.
(I know, I fib just a little bit. There's no supported RPM of perlbrew available for CentOS or RHEL. What can I say? I'm an idealist. At least it's only seven short years before the Perl 5 world can rely on Enterprise Distribution users being able to use tools such as perlbrew.)
This is still a big job, so the Perl 5 world needs even more people to donate their time and skills and effort to making sure that code written and donated by other volunteers continues to meet the needs of people paying third parties for the privilege of installing RPMs that are guaranteed never to change for seven to ten years.
Fortunately, this is an easy process to automate with Perl 5. I have some proof of concept code which will test a distribution against all supported versions of Perl 5. Sure, it takes quite a while for each test run, but computers will be faster in seven to ten years when I can release it. (I'd release it now, but I was lazy and used named captures, a Perl 5.10 feature. Won't it be nice when we can use those? Sorry my code is unusable by everyone else.)
I get shivers just thinking about how wonderful 2018 will be, the year of Perl 5.10.