Well we're two days away from the Keynote and nothing important has leaked.
At this point, Apple may have to leak something themselves tomorrow, if they want crowds to watch.
I don't recall a WWDC that was so unanticipated, the discussion thread here wasn't even started until less than 48 hours prior.
Personally, I expect updates to the whole family of Apple operating systems.
In terms of hardware, I want to see what happens with the Pro, and also if the Watch gets any new significant health features.