We have them now! From your GP comment > (available now as separate coins, coming soon-ish to ETH, and probably at some point to BTC) See Zcash, Zclassic, Mo

We have them now! From your GP comment > (available now as separate coins, coming soon-ish to ETH, and probably at some point to BTC) See Zcash, Zclassic, Monero, etc. The tech behind Zcash is called ZKSnarks is available for use in ethereum smart contracts as well.