The whole concept of Perl 6 frightens me. I fear that I'll have to relearn large chunks of the language. I fear that I'll have to do a major porting effort on my existing code should Red Hat, Sun, or SGI decide to ship with Perl 6 instead of 5. It's not so much that I fear change, just big change.

It would be a disaster if installing Perl6 broke all Perl5 scripts. Since Larry has no desire to author a disaster, he has mandated that Perl6 be compatible with Perl5. The compiler will only go into Perl6 mode when encountering some Perl6 construct, like 'module'.