Some people want to use Composer to install/manage their Drupal site. We have already many core issues around this topic. A important part in the composer ecosystems are package repositories. These repositories store information about all available packages.
Drupal does not use Composer to specify dependencies between Drupal modules and themes nor has every module an additional composer.json in its repo. Therefore we build a composer repository for the Drupal community which converts info files to a composer.json. This repository is hosted on https://packagist.drupal-composer.org/ and contains all modules for Drupal 7 and 8. (The source code is on github https://github.com/drupal-composer)
We use different sources to get updates from modules (e.g. releases.tsv) but thats not an ideal solution because its not fast enough and the package definition is already a little bit out of date.
Technically speaking: I'd like to use a post-receive hook on drupal.org infrastructure to get information about any change in any module.
Is this a feasible solution? Maybe one day, if Drupal uses Composer for Module dependencies we could move the whole project to d.o infrastructure.
Thanks to everyone who contributed to drupal-packagist so far especially winmillwill, derhasi, davidbarratt, kasperg, tstoeckler and greg.1.anderson.