The last iMac was released back in October of 2015.
According to MacWorld iMac predictions include new graphics chipsets: Polaris 10, by AMD, which may make the next iMacs VR-ready.
If Apple does manage an iMac update prior to the end of 2016 it could feature Kaby Lake processors, but Apple skipped Broadwell and delays are common the chip sector. Kaby Lake chips supports Thunderbolt 3 and native USB 3.1. However, the chip won´t support DisplayPort 1.3.
It's likely that Apple's next generation of iMacs (or the higher-specced models, at least) will be equipped with graphics chips from AMD's Polaris set, which were announced at the beginning of 2016.
WCCF Tech said that AMD got 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 noted these processors will appear in "new desktops and notebooks from Apple, which the company plans to reveal to market later this year".
Apple's current iMac line-up have AMD Radeon graphics chipsets as standard in the 27-inch models. The 21-inch models come with integrated Intel Iris Pro 6200 graphics.
Rumors say that the iMac 2016 will be released alongside the iPhone 7 this September. However, the Kaby Lake won't be available until the end of the year. which means that the iMac may not be coming this year.
