Perl 6 classes should be able to inherit from perl 5 classes--this isn't any different a problem than inheriting from Java classes or .NET classes. Going the other way may be more problematic, but we'll see.

When you inherit from a perl 5 class, you'll treat the inherited portion of the object as if it were opaque, which is probably the best thing to do in an inheritance situation in general, and parrot will handle the automatic delegation in such composite objects.