Though it strikes me that with such an extended chain, it'd be better to essentially have ping-backs for each item that referenced or used the data.
At least with stuff like this there aren't privacy concerns, and it's not a low-level web commodity like a picture. EXIF & IPTC data can show authorship, but can also store location data, and whatever crap you (or your software) decides to stuff into metadata. It pisses me off that tumblr strips metadata, but all-told, it's the best course of action anytime people use your platform to post erm.. selfies.
Has anyone here found good ways of battling sites that "repost" content without attribution?
More serious you are fighting a losing battle here. If even the big media companies with full time employees can’t stop this it is basically impossible.
Google might be able to do something about this if they banned sites that continually re-posted content without attribution, but even here you would have issues - you would not want to get into the situation where because of the time google crawled your site you were accused of stealing from the reposter.
I'd say it mighty even be useful for silly articles like the one he started with, but for anything more serious, with several sources, those solutions to crediting a single source are but a joke. a lame joke no less.