At WWDC 2020, Apple confirmed that they would begin transitioning to their own custom silicon. The company expects this transition to complete over the next two years, but did state that the first ARM-based Macs will be arriving later this year. Kuo’s report would suggest that the iMac could be that computer (his previous report also suggested that the 13-inch MacBook Pro could be one of the devices as well).
Apple did not announce any new hardware at WWDC, but that isn’t surprising given that WWDC is generally software focused. This means that if and when the new ARM Macs are announced, it would be announced at a later date in the year at a separate event. Oddly enough, Kuo does not mention whether or not the 27-inch model will also be receiving a redesign.
However, he does state that Apple will most likely refresh its existing Intel-based iMacs in the third quarter of the year. Whether or not the redesign will be part of the refresh remains to be seen, so take it with a grain of salt for now.