The phrase "and WikiDev '16 established as an opportunity to settle many stalled issues" could probably just be turned into a success metric itself. Eg: "The Wikimedia Developer Summit is seen as *the* opportunity to settle many stalled issues by all Wikimedian developers."
Topic on User talk:RobLa-WMF/Blog
No idea how to measure that, though, especially by the end of Q2 (or even Q3).