I don't see why Perl needs interfaces in any form, they're just there to satisfy the compiler in statically typed languages, aren't they?
No they're not ;-) Not if we're using the term as used in Java land anyway. They're a way of talking about common behaviour that cuts across class hierarchy boundaries.
In Perl 6 they're subsumed by roles (a Java interface would the equivalent to a role without any implementation code.)
(Note: Apply my standard "I've not read A12 properly yet" disclaimer to the previous sentence, but I'm sure chromatic will correct me if I'm wrong :-)