While I do agree that there is a need for a real packaging system for PHP, I don't think Composer/Packagist is the answer.
Packaging is a real hard "exercise", I've dabbled with it, and it's certainly not an easy problem. Composer/Packagist is still not there yet and its ties to Symfony are "scaring" off developers (myself for example).
If it wasn't for the outdated code, the bad peer review system, PEAR is the closest thing we have, as PHP developer, of a working packaging system. If only the PHP team would invest a bit of time to modernize it and make it relevant again, I'd give it a go for sure.