The 2013 Mac Pro
Shortly after WWDC 2012, Tim Cook replied to a pro customer who'd emailed outlining his concern about the lack of a new Mac Pro: "Our Pro customers like you are really important to us. Although we didn't have a chance to talk about a new Mac Pro [at WWDC], don't worry as we're working on something really great for later next year."
A new and radically rethought pro machine - extensible but not a giant like the old Mac Pro - would undoubtedly go down well at WWDC 2013.
Happily for fans of the Mac Pro, Apple's Pro project manager Douglas Brooks let slip that "something really different" is on its way.
Although such a thing being a niche (pro market) within a niche (desktops) within a niche (Macs) in Apple's books might scupper its chances, regardless of Cook's promises.
- See also: Has Apple abandoned pro users?
Retina iMac and Retina MacBook Air
Sooner or later, high-res displays will be the default. Apple tends to lead in such things rather than play catch-up, and its MacBook Pro line's currently transitioning towards Retina displays.
If Apple's going to make a dev-oriented Mac-based hardware announcement at WWDC 2013 that doesn't involve the words 'new Mac Pro' and doesn't merely entail minor upgrades, Retina displays for the MacBook Air or even the iMac could become a reality. (On the latter, it's even possible that could be Apple's new vision for a 'pro' Mac, as much as that would irk certain professionals.)
In early June, SKU-based hints were dropped that the MacBook Air would be getting the high-res Retina display at WWDC - unless it turns out to be another Retina-toting MacBook Pro.
What we won't see at WWDC 2013
A single merged Apple OS
Whenever rumours appear about Apple welding another bit of iOS to OS X, pundits inevitably claim that, eventually, Apple will only have a single OS for desktop and mobile.
But Apple cares more about user experience; it's not conceivable it'd shoe-horn a desktop OS on to iOS or force desktop users to work with something entirely designed for mobile and touch. Perhaps in a decade, the argument will be moot, Macs will be gone and everyone will have an iPad 10 glued to their face, but until then, OS X and iOS will remain separate.
A new Apple television/the mythical iTV
We're sceptical an Apple television will happen. People rarely upgrade TVs (Apple likes people who regularly buy hardware), margins are razor-thin (Apple likes margins), and the industry's under pressure from the so-called second screen, a business in which Apple already does rather well (Apple likes this also).
If an Apple television did appear, it'd almost certainly be iOS-based, and so any 'announcement' at WWDC 2013 could be sneaked in under the radar, as part of a general Apple TV SDK. The hardware could then be shown off at a separate event.
The iPhone 5S, iPad 5 and Retina iPad mini
Although WWDC 2013 will undoubtedly provide us with insight into iOS 7, we doubt very much any new iOS hardware will be unveiled (although it might be possible to guess at new features, if software demos make them obvious).
Our reasoning: despite gaining a certain amount of coverage in the press, WWDC remains a conference for developers, and a new iPad or iPhone would warrant its own show, where it didn't have to share the stage with anything else.
Also, we might be tempting fate a bit here, by stating clearly that Apple definitely won't unveil a Retina iPad mini, because, man, we'd look so stupid if Apple unveiled a Retina iPad mini that we definitely don't want. Therefore, Apple absolutely won't unveil a Retina iPad mini at WWDC 2013. (Crosses fingers.)
An Apple iWatch
Wearable tech! It's the latest thing, what with Google's sci-fi specs and smart watches people mostly don't care about! We think it's pretty unlikely an Apple watch will ever appear, but, again, like other iOS devices it would warrant its own special event.
It's not going to show up as second billing to the next version of OS X, after an Apple exec's got all excited about something new and technical that iCloud's totally supposed to do (and, in the event, probably won't).