All rotating around zend, refs, memory, these variable's copy...
Good question: Who cares about Zend?
I monitor my application under kcachegrind and xdebug/tracefile-analyser.php: in generally its array-copy operations, classes load, require/include, and strings and its definitely are slow. Why no types like: lists, tuples, ascii-string (I think it fastest, than unicode or any latin)? Array its multi-paradigm? Ok. Nice YAGNI implementation.
I try prevent pass arrays and replace it with ArrayObject or stdClass or any custom object because objects its reference by defenition. It help improve memory consumption but not so effective.
I think PHP needs improve internal components first and also Zend that nailed down to PHP.
But its good of course that spec under public discussion, hope this help improve language.