Nested statement modifiers are reportedly rejected by Larry for Perl 6, so presumably ruled out of court for Perl5 as well. Poking around shows this thread
about a year ago, with someone citing Larry rejecting them 5 years ago
If indeed this is final, all I can say is "too bad". I think all the arguments against multiple statement modifiers apply equally to single statement modifiers. And you may call it "enough rope", but rope can be awfully handy at times. If I have time, I may dig up a couple of examples where I would have used them, and people can laugh at me.
Update: another couple of Perl 6 threads, from 2003: Statement modifiers, Statement modifiers (yes, again)