experimental.pm handles both enabling features via feature.pm and disabling the experimental warnings for them. The features it supports aren't the exact same features as exist in feature.pm. Some of the things it supports don't need to be enabled, but do issue warnings. And some things do need to be enabled but didn't issue warnings on older versions of perl. experimental.pm is also a dual-life module, so it supports some features even though the perl it ships with no longer supports them. That should probably be more clear in the documentation.
autoderef never needed to be enabled, but it did issue warnings in perl 5.20 and 5.22. There is a bug here though. It should be throwing an error if you request autoderef on a newer perl, rather than silently doing nothing. I've filed a bug for this.