Well, there's already ample precedent for "ugly names like that", such as __DATA__ and __PACKAGE__. Programmers need all the help they can get at the time of devising useful typographic conventions for identifiers, since the good alternatives are so few. One of these few good alternatives is the all-cap identifier, and I think it is a shame that the core has declared it off-limits.

Update: Besides, the core can still reserve specific all-cap identifiers such as the one you list, just like it reserves any other specific keyword (if, else, for, etc.). My objection is to the blanket claim on all all-cap identifiers.

I think that the specially named subs deserve having beautiful names. OTOH I don't consider __DATA__ and __PACKAGE__ to be "ugly names" at all. They're nice as special tokens, and I must say I regret they (being supposed) not to be there in Perl6.

As Larry himself wrote once, the shebang line

#!/usr/bin/perl
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is much like a "hello!" and the

__END__
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line is much like a "goodbye". Now IIRC it is supposed to be taken away in favour of a pod (or whatever it will eventaully be called) directive. But I mean: maybe it's just me, but I'm really keen on that "__END__".