So October 2016 is the most likely date for a new iMac launch, then? Not so fast.
Apple's yearly cycle is built around three major press events: autumn - usually September (new iPhones and iPads); spring - usually March (new iPhones and iPads, sometimes MacBooks and watches); and summer - usually June (WWDC - operating system updates, and occasional hardware). But that doesn't mean the company stays quiet the rest of the year. Mac updates can be folded into the big three events, but they're often launched at their own smaller launch events. The iMac update in 2015 got its own announcement, a few weeks after the iPhone 6s reveal.
The iPhone 7 will most likely launch in September 2016, and it's possible that Apple will lump new iMacs in with that event. Whether it does this, or updates the iMac at its own event, or an event dedicated to new Mac hardware in general, will depend on how major the hardware update is going to be. A separate event would imply that Apple has something big up its sleeve.
But bear in mind that, unlike the yearly or event twice-yearly update events we're used to for iOS devices, desktop Mac refreshes have frequently come several years apart. WWDC 2017 (which will take place in June next year) is therefore a possibility, and we may have to wait even longer than that.
Still, we'll try to remain optimistic. Watch this space for clues and analyst predictions about the next iMac update as soon as they appear.
It's believed that Apple's next generation of iMacs (or its higher-specced models, at least) will feature graphics chips from AMD's Polaris set, which were announced at the start of 2016.
WCCF Tech reports that AMD won the contract last October but was only able to get confirmation from additional sources in April 2016.
The contract is for two chipsets: Polaris 10 (previously known as Ellesmere) and Polaris 11 (previously known as Baffin), and WCCF Tech says these processors will appear in "new desktops and notebooks from Apple, which the company plans to bring to market later this year".
With the MacBook and MacBook Air having recently seen updates, and the Mac mini highly unlikely to incorporate a discrete graphics unit, the remaining candidates are the MacBook Pro, iMac and Mac Pro. MacRumors reasons that the power range of these chips makes Polaris 11 a strong fit for the MacBook Pro, while Polaris 10 suits the iMac.