That's an interesting idea. One of the things we are building is a "reddit like system"[1], and so I could see building a feature like that. Our current focus is on enterprise usage, though, not building something for the public web. But the code is all Open Source, ALv2 licensed and it's done in Groovy and Grails. If anyone is interested on hacking on something like that with us, just shout.

[1]: https://github.com/fogbeam/Neddick