mneale I think hovers is tough here. I would expect this to be a screen that folks would want to project on a big screen somewhere in their team area. "Broken since" which is what the red stage dots would show would be super helpful information.
Here I have added another state indication to show the stage didn't run this time (it is semi-opaque). To me, adding a gesture adds at least as much complexity and user burden as showing the combination of a number and a color and maintains the 'hands-free' use cases.
The Nokia guys also include time to complete stage within each stage circle, as one of their uses cases was pipeline CD optimization. They wanted to see at a glance how long the total run took and which stages were slow. They were expert users and designing specifically for themselves, but I found the few things that they showed immediately on the screen to be fairly compelling, generally. They wanted 'at a glance' diagnosis so they could project the results to a group and flip quickly between pipelines.
...anyway, that is my caution.
I think past stage failures is a really important bit of health information worth getting 'at a glance'. Stuffing important information into hovers, I doesn't always reduce user complexity, in fact, often it increases it. ...thus I would look for other places to trim clutter, if this feels too cluttered.
greiber just to make things more fun - what about unstable build states...