Why wouldn't Wikipedia be a great source for future cultural historians? Assuming the edit logs and other aspects can be traced then it'd be a treasure trove of information on points of contention in national and international contemporary historiographies and points of contention in contemporary society. The very fact there are so many competing wikis is a fantastic indication of modern 'tribes' attempting to control their members view of the past and present.

Anyway, I don't see an issue with these sites on the whole, you'll just have to develop a methodology for spotting fraudulent entries and biases among the authors. It's not like we don't have to do this with our more traditional sources anyway.

I've tagged this as META for now, but just to clarify: are you asking about the site being acceptable as a source by this subreddit, or for an academic paper?

Personally, I find that its entries (especially if you're only going to go for confirmed entries) are created far too slowly. Memes move and evolve rapidly - most are there and gone within a week or two, only a few really tend to endure and filter away from their original site (though those are probably the ones you'd be more interested in).

With that being said, I'm not sure if the blog Meme Documentation on Tumblr is much better, since again they can be a little slow, and they're only documenting from one site. I don't know of any other sites that are dedicated to actively documenting memes; you'd probably only find those very prominent or enduring memes on Wikipedia.

So it's a useful resource, but I wouldn't rely on it too heavily.

(For academic purposes I've always been told to attempt to find the original source. That can be quite difficult with older sites, but KYM usually links to the earliest known instances so you could use their links.)