Well, that makes a big assumption. The assumption being that there will actually be a Perl5 release before Perl6. It's been almost a year since 5.9.1 was released, with no 5.9.2 appearing at the horizon.

In the now almost 5 years perl6 has been discussed, only one feature has appeared in the 5.9.x track: the defined or. And that's something that has been requested for years before the perl6 project started.

Other than a few modules that use tricks like source filtering or overloading I don't think much of perl6 will trickly into perl5. Perl5 development, slow as it goes, seems to mainly focus on improving existing features (threads, Unicode, regexes), and then mostly below the surface (removal of bugs, better performance, reentrance). I get the impression (correct me if I'm wrong) that perl developers either work on perl6 or on perl5, and that only a few work on both.

So, for various reasons, I think it's unlikely much of the perl6 goodies will get implemented into perl5. Which is a pity.