Since it's aiming for Linux, I wish there was a comparison to two similar technologies: toolbox and plain systemd-machine. I'm not sure if dock provides anything they don't?
But you are not correct in assuming this is aiming for Linux - my next goal is adding BSD jails. I see absolutely no reason why different container engines would bother user with architecture, different APIs and apps etc. And, then, I think there's actually something, that although it sounds crazy, might work wonderfully on any OS, see my comment here: https://news.ycombinator.com/item?id=31625920
That seems pretty much entirely unrelated? It just is a software project that happens to be distributed by the same umbrella project.