From a development point of view (which is what the focus of the event is primarily for), I hope that they add some dynamic support to Swift, I really have a problem in passing unchecked strings around instead of type checked references. Thats the main thing I want, other than that making UXKit public for OS X would be nice so I don't have to deal with AppKit, and possibly some NFC API's and native WatchOS apps support would be welcome too.
From a consumer point of view, I just want stability, efficiency and security updates, it's been long overdue as the main focus has been feature pushes for the past few years, primarily in iOS rather than OS X. By the sounds of things this will be the case if the rumours are true, but I do hope that they will bring surprises too, and knowing Apple, they normally do!