The Internet is full of conjecture and predictions for the WWDC Keynote. Instead, I'd like to point out a few things I'll be looking out for:

Siri Commitment: There's lots of rumors about Siri getting some improvements. However there are improvements and there are Improvements. It's been years since Siri was first announced and we have yet to see anything more than incremental steps. If/when they announce new Siri improvements, look to see if they are the kinds of things that took three months or three years to create.
That Pesky Apple Watch: Lots of people don't like their Apple Watch. (I still like mine.) The processor speed still feels like the bottleneck to me. If they announce watchOS with new features and improvements, how do they address that the current hardware has lots of trouble with the existing OS. I'm sure this will get fixed/improved with new watch hardware but I don't expect that to get announced at WWDC and they still have that issue on the table.
Dark Mode(s): It seems like apple is thinking a lot about how our screens look at different hours of the day. Looking at the signs on Moscone, I expect a dark mode is going to be seen most likely on iOS and (hopefully) Mac too. Will this be made out to be a big deal or just a passing point?
Loose Lips Sink Ships: One thing just about everyone in San Francisco agrees upon is that this year there aren't nearly so many leaks and everyone is expecting a surprise or two at the Keynote. That's a good thing. Christmas morning is no fun if you've already peaked.
Stagecraft: Apple now has four separate platforms (Mac, iOS, watch, and tv) to address. Last year's WWDC keynote felt pretty self-indulgent at times. It will be interesting to see if they tighten up the presentation this year.
As always, enjoy the show.