Putting it in the Bitcoin chain itself is a hard-sell because there is a serious scalability downsize (all the cryptographically strong anonymity techniques break pruning), among other pedestrian reasons.  A side-chain using it seems virtually certain to me, limited more by the deployment of sidechain tech than anything else... even more so than the ZeroCash anonymity design simply because the ring signature approach is so simple by comparison.

But it's all a guess at this stage. Technology progress in Bitcoin is slow— for good reason— and now with the prospect that altcoin pumpers may we well funded to try to disrupt that progress… well, it'll be sad if what kills cryptocurrency isn't competition from traditional financial instruments or authorities but just poisonous behavior between competing systems. :-/