I created my first open-source Symfony bundle: PlaceholderBundle. It is an abstraction of Primitive and/or SQIP for use in a PHP respectively Symfony application. This way, you can automatically generate nice & adaptive placeholders for images in the format you like, all in your PHP application or your Twig template. Refer to the documentation on how to use the PlaceholderBundle. For now, the underlying nodejs packages still have to be installed separately, depending on which you want to use. The configuration allows to personalise the placeholders as much as the underlying applications allow it.

I will write a follow-up on how to begin with developing a third-pary bundle, as I think the resources for it are rather limited. A general tip is to checkout existing bundles on how to do it.