Hmm.. I was wondering if we should go one step further and also provide a stream to the data. If the most common usage of this construct is going to be reading the data after __HALT_PHP_PARSER__ then we should optimize for that case. Something like
<?php
$data = gzdeflate(file_get_contents("php://data"));
?>
<?php __DATA__; ?>
...
I would suggest keeping such implementation in the user-land code rather then the core. It would be fairly trivial to implement a streams wrapper to do this and it can internally handle various decoding schema like decompression etc...
Ilia