I don't think this is necessary. The solution is to go to your project's mailing list, irc room, ask your twitter followers, or whatever, and ask for a new maintainer. Even messaging the users who actively report issues can be a good idea.
Once you have a new maintainer, announce it, open a support request in http://support.github.com asking them to re-root the network to the new maintainer's fork, and then change the description of your repo (a one click change) to something like "this is no longer maintainer, check http://github.com/otheruser/repo
Yes, it takes a while, but then when you solve it, you give the community a new maintainer. So I think it's a better solution than just marking it as abandoned :)
Once you have a new maintainer, announce it, open a support request in http://support.github.com asking them to re-root the network to the new maintainer's fork, and then change the description of your repo (a one click change) to something like "this is no longer maintainer, check http://github.com/otheruser/repo
Yes, it takes a while, but then when you solve it, you give the community a new maintainer. So I think it's a better solution than just marking it as abandoned :)