Yeeyan, Songshuhui and Douban
(I thought you were afraid of their possible competition at first sight = =)
Well, as for cooperation or learning, I think it may be quite hard.
The spirit is hard to change. WP, YY, SSH and DB are all totally different things, like horse and zebra. So it'll be weired for WP editors to just translate passeges, or to write thesis focusing only on one point, or to express their view as if they were in a forum. No, none of them are WP. WP is very formal, with strict format rules and copyright rules and strateges. It is free, but not as free as them. Of course the not-so-free spirit keeps many new WP editors out, but if you're not going to change the 3 main strategy, I think it have to.
And it may be hard for people of YY, SSH and DB to give a hand to WP, because there is no time. Time is already too little to focus on one website, not to mention two.