As per the compose report:
the 'docker' package is missing from the x86_64 Server and Cloud install trees, and hence from the Server DVD.
This appears to trigger an anaconda crash on the Server DVD:
but even if anaconda didn't crash, the Server package set would not be installable, hence I'm nominating this as a blocker rather than that. Criterion: https://fedoraproject.org/wiki/Fedora_22_Alpha_Release_Criteria#Package_sets - "When installing with a release-blocking dedicated installer image, the installer must be able to install the default package set."
Also, there have been no Docker image tarballs since http://dl.fedoraproject.org/pub/alt/stage/22_Beta_TC2/Docker/x86_64/ as far as I can tell.
https://admin.fedoraproject.org/updates/docker-1.5.0-25.git5ebfacd.fc22 is the fix for this, apparently.
Discussed at 2015-03-30 blocker review meeting: http://meetbot.fedoraproject.org/fedora-blocker-review/2015-03-30/f22-blocker-review.2015-03-30-16.04.log.txt . Accepted as a blocker per criterion cited in #c0.
The update has been pushed stable, and TC6 had no repoclosure problems. Closing.