Speculation has it that there will be new versions of Apple's iOS operating system for the iPhone and iPad, along with watchOS for the Watch, and tvOS. There could (and should) be updates to the macOS desktop operating system and Apple's iCloud, Music and other cloud offerings.
Will there be new hardware? Apple's not as good at keeping schtum about what it'll announce at events and conferences as under Steve Jobs, but it can still spring surprises and unveil new products, sometimes at the WWDC too.
Even so, I'm going to take a punt and say a new iPhone, if there's one coming, will have its own launch event after beta testing of the new iOS has ironed out the bugs. The main argument against this is if Apple releases iOS betas at the WWDC, curious people will be able to go through the software to work out what new features will show up on a new iPhone.
Unverifiable leaks suggest that the new iPhone will do away with the home button at the bottom of the screen, which kind of makes sense: Apple already swapped out the mechanical button for a non-moving gizmo with the buzzy Taptic engine mimicking the feel of presses, and which can be programmed via software.
A smooth area with no button depression would look cool, but how would Apple implement the Touch ID fingerprint scanner on iPhones? Perhaps several areas of the screen (that's meant to be an OLED) will be able to scan fingerprints?
Today's iPhones are very good indeed. Looking back on a decade though, the first iPhone is a reminder that Apple isn't that different from other companies, only perhaps more lucky than most. The first generation iPhone didn't even support 3G back in 2007, was pricey, but it looked great and was nicer to use than just about everything else at the time. It sold in millions.
An iPhone without the apps ecosystem is unthinkable now, but Steve Jobs apparently wasn't sure about letting third-party developers on board at first. He changed his mind a few months after the original launch (and borrowed Nokia's idea of digital certificates for apps to verify developers), but it took until 2008 for the App Store to arrive along with 3G support for the iPhone.
Although the new iPhone was very cool, it wasn't guaranteed that Apple would have a hit on its hands with the App Store: Apple wasn't first with smartphones or apps, and the first iPhone was quite limited compared to what was available at the time.
Nokia had apps, developers, great cameras and fast data for its devices but design, and usability beats heaps of hard to use features every time. Apple knew this, but Nokia never figured it out. Which must've seemed bizarre to Apple at the time, because Google got the message with Android and kicked off its own giant smartphone business while Nokia choked and croaked.
Ten years on, nobody questions that design and usability are king. And that'll make life more difficult for Apple, as it'll have to reinvent itself to remain unique. This year there will be lots at stake for the company and Apple bosses are probably starting to feel a tiny bit clammy already.