Incredibly, an effort lead by Flávio Soibelmann Glock is working to actually implement Perl 6 in Perl 5. You can download v6 now on CPAN to try it out. Its feature set has not caught up with pugs yet, but there is steady progress on it.

Perl 6 features are also coming to Perl 5 in other ways, see Perl 6 for Perl 5.