OS X 10.10.4 shipped today, and as expected based on the developer betas, Discoveryd is gone, replaced by an updated version of good old mDNSresponder. At WWDC, word on the street was that Apple closed over 300 radars with this move. Not dupes — 300 discrete radars.
Three hundred individual bugs fixed simply by reverting to mDNSresponder shows just how flaky discoveryd really was. Shocking.
Also in 10.10.4:
From the bottom of my radar #18927527, thank you.