I know of many users who would recommend a FD but all of those users have not tried the same Mac with a HDD. Most compare their FD iMac to a much older HDD iMac so it's not exactly a fair comparison. I have the 2013 21.5" iMac with a HDD and find it great

It boots up in around 30 seconds which is around double that of the fusion/SSD alternative but most Mac users only restart once in a blue moon so I never see that being a factor. As for app launching times, I have hardly any difference between my iMac and a similarly specced MBP retina 15" with an SSD. This is because once an app has been opened for the first time, parts of the app are stored in RAM so that it can launch faster the next time it is open. So in really terms, opening an app on a HDD may take 2 seconds longer than on the FD for the first time after a restart, but after that they will be so close that it would be a tie.
As for an update to the iMacs, I don't see any changes to the 21.5" iMacs, just a 5K 27" iMac.