How to set up remote updates

WordPress has a fantastic auto-update system both for core systems and WP-hosted plug-ins. Is it possible to use a similar system to update files that aren’t hosted on a WP-controlled server? Something along the lines of an alternative plug-in repository.

I’m wondering whether someone has already worked on something like this, whether someone might have a deep understanding of how the core WP update systems work, or if a few developers might be interested in collaborating on an open update framework. Any ideas or takers?