I would like to be able to define a function with a 
referenced argument as well as give it a default value.

function foo(&$bar = NULL) {}

So, what will it reference, you ask? Nothing. I just want 
the argument to be optional, but to reference if there is 
an argument supplied. So, it's less of a default that's 
needed for references, more the ability to have the 
argument be optional.

This would make me so happy.