The nested modifier, while it may have already been rejected, could have some tidy little uses.

s/foo/bar/ for (@these) if ($this);
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I suppose that could be accomplished as

map { s/foo/bar/ } @these if ($this);
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but is that as clear as the first statement? Using map in void context to get the effect of a for seems clumsy.

As for something I'd really like to see, interpolation of method calls in a string.

print "The 'bar' attribute of object 'foo' is $foo->bar();\n";
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As it is, I get to do the oh-so-readable

print "The 'bar' attribute of object 'foo' is @{[ $foo->bar() ]};\n";
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That doesn't look like it should work, but it does.

While I'm on the concept of OOP, I think I'd like to see Perl actually implement some form of strong encapsulation for objects "out of the box" as opposed to having to roll your own or re-use your "tried and true" method, whatever that may be (CPAN or home-grown).

Certainly the "defined or" (dor) functionality would be a serious benefit to prevent warnings in my code.

That's about all I can think of at this late hour. Time to sleep.