When I first /msg'ed you to inquire whether you saw any differences, I at the time didn't either, and it wasn't until I investigated further that I realized there should be a fatal runtime error (and there is) with the non-unpacked version.
Anyway, you present good arguments, but I am stubborn against considering it a new Perl idiom that should find its way into real code. I do like Moritz's "use perl6" version, because of how explicit it is, but still have concerns. :)
Anyway, great RFC, as it produced good comments.