One of the biggest challenges I have as an interviewer is setting up a framework that allows me to compare candidates fairly. Most candidates don't have a list of open source tasks they're working on. If I have three candidates who completed my standard interview code sample and your open source pull request, it's much easier to spot the differences in the other three candidates.

This is absolutely brilliant - I think that this is the way to go for hiring tests! Either that or you get paid for the hours you put in.

This is a very good idea! I could even imagine something like this could be a socially acceptable way to test candidates, with thw benefit of helping open source