Again, I'm going to mention Ethereum and Metropolis, and reiterate that there are a lot of unknowns, but most of the development can be followed. it seems to be approaching completion, maybe a month away, maybe longer. They never gave a fixed release date but August was suggested as a rough estimate earlier this year. If they are behind schedule, all the better it means they are being meticulous.
https://z.cash/blog/project-alchemy.htmlhttps://forum.z.cash/t/cross-chain-atomic-transactions-project-alchemy-stellar/13524https://blog.ethereum.org/2017/07/08/roundup_q2/(the audio is a bit distorted, video is long, but, it's pretty complete.)
https://www.youtube.com/watch?v=n8zsPf4FzO4I believe the Zen chain is currently implementing something similar. Still, what remains is that Zero has a faster block time, and I believe it can handle more transactions per block, all the other extras are a nice touch to in this inter-chain future.