What problem does this feature solve?

It would encourage and inspire a lot of developers if the repository would be opted-in to the hacktober event.

What does the proposed API look like?

Considering how Hacktoberfest is going this year (see: https://twitter.com/shitoberfest), I personally think we should not put a spotlight on this repository for now.

I agree, that there are some trolls/spammers, but I think people wouldn't dare to do it in such a large repo + shitoberfest only collects the worst examples, the majority of the participants are actually contributing