@smooth : Is a quote from 2 years ago still worth something now ?
It wasn't entirely based on a quote, but also on some discussions I've had with people who understand the cryptography better than I do. I read the section of the paper coins101 posted and the modification to provide privacy against unbounded opponents seems to require a private (and guaranteed secure) side channel. I'm not sure how that is going to work in practice; it seems like a significant deviation from how cryptocurrencies normally operate. I'm not saying it couldn't be worthwhile, but many details would need to be worked out.
@coins101 : To answer coins101 on zerocash implementation, it looks the good way to go yes.
From start it has been announced that shadow would prefer a zerocoin implementation over ring signs when that tech will be ready.
I can confirm they have stated this is various (public) discussions with me over the past couple of years. Of course having a goal and actually implementing it are two different things, but I wish them the best with it. I expect there will be quite a few people working on different Zerocash implementations, not just the Zcash one that seems to be getting a bit of hype now.