I've just read the other suggestions. That kinda taints my answer, as I'd have said: "I'd want to remove (as far as possible), the inconsistencies and arcana that I'm no longer aware of because I've memorized them by now, but which took quite some time to learn".
Actually, I think the changes I'd most like to see revolve around making perl a bit friendlier towards functional and OO programming. Function/method definition and invocation could be less verbose. See for example Method::Signatures for a step in the right direction (Moose is lovely too, of course).
update: Oh, I forgot! I would absolutely love to have lvalue methods that work. I'm getting really tired of having to write $foo->bar( $foo->bar() + $wibble ). I'd like to be able to use more syntax than just ->() once in a while.