Snapcraft 2.1 is described by the Canonical developers as a "risky and ground breaking release" as it introduces the concept of "skills". Snapcraft 2.1 also now allows uploading of snaps via the Snapcraft client. Snapcraft 2.1 also drops a number of its base dependencies.
More details on Snapcraft 2.1 can be found via this mailing list post and Snapcraft on Launchpad. If you are unfamiliar with the ongoing work around Snapcraft/Snappy in Ubuntu, see this developer.ubuntu.com area.