... the Traits paper... did not mention ... how traits (Perl roles) improves on ... prototype-based programming. (paraphrased)

Note that the approach described by the Traits paper is a fairly general concept, and Perl 6 will not be blindly following their recipe.

I would expect that Perl 6 will support a delegation scheme that looks like a prototype-based system. The problem/goal is to enable this approach and others, so that you can combine a logging aspect and an exception-handling role with a access-control proxy, or whatever.