I don't think Canonical has even done its homework before going full-steam on Snappy. They seem to have completely ignored the Nix and Guix projects, which also offer atomic installation and rollback of software, but without many of the flaws that Snappy seems to have like application bundling (duplication of dependencies amongst packages), package namespace issues (identifying packages by name+version+developer, not a cryptographic hash identifying the
precise build), duplicating packages in home directories via unprivileged package installation, and more. Pretty much anything Snappy can do, Nix and Guix do better and then some.
This blog post from a Nix hacker does a good comparison to show the issues: http://sandervanderburg.blogspot.com/2015/04/an-evaluation-a...