Conary is/was interesting. I had high hopes for it when it was released, but that was years ago now. Whether it was the concept wasn't as great as I thought or just that rPath didn't have the resources to make it I don't know.
But I did not see Conary as the same as Nix/zero-install (and still don't) because to me the idea behind rPath was that you could manage a largish number of "small" changes well (ie. 1,000 customers with a small number of patches each), that package creation might be easier than anything else, and of course the rollback/sub-set features (although years later others are getting there).
Nix/zero-install/etc. seem to me to be based on the idea that you can have large changes within a distro. and it still work. And I'll bet against that everyday, and twice on Sundays.