R.e. server vs desktop, I would say that desktop users / daily driver users should be on the unstable channel. There is simply too much desktop software for backporting to be realistic with the current workflow. And considering that Arch Linux and its derivatives are often recommended for desktop users, the rolling release model can work well for the desktop. There is enough quickly-expiring software (browsers, chat clients, etc.) that the stable version is more often broken than unstable, in terms of usability.
I think the real issue though is the release being delayed due to strange software problems. This is similar to unstable being delayed (New Merge Policy for an always-green hydra). In both cases, the only real solution seems to be to ensure someone is actively working on fixing these failures; maybe the NixOS foundation could hire a release manager, or put up bounties on release-critical bugs.