It seems https://hydra.nixos.org/job/nixpkgs/trunk/unstable#tabs-constituents indicates there are many successful builds.
Not now (anymore?), as far as I can see. Occasional failures are quite common.
Sometimes the channel scripts are not running. howoldis.herokuapp.com says that it is still an old commit:
Right now that seems correct. I see a couple queued jobs for all evals from this week (roughly), so it’s supposed to wait for them finishing.
EDIT (after a few hours): let me cancel those now, as they might not finish anytime soon (not sure why they’re stuck) and don’t seem worth delaying channel.