Very similar to what Knuth did with Tex. I like it.
Actually, I think that, for exactly that reason, it's a wrong idea. Knuth's numbering is meant to suggest that, except for minor corrections, TeX is in its final form. I can't imagine Larry Wall ever feeling that way about Perl.
At his FOSDEM talk, he actually talked a little about how Perl 6 should be flexible enough to keep on changing basically forever... given that you can edit the parser even on the fly, it seems plausible.