Sounds like it may be awhile before we see an iMac update. The latest article seems to indicate a possible MBP update before years end but there's still no solid info on the iMac update. I may just get a 2015 iMac 27 and call it a day.
https://www.macrumors.com/2016/10/11/mac-sales-continue-to-slide-amid-lack-of-updates/
https://www.macrumors.com/2016/10/11/mac-sales-continue-to-slide-amid-lack-of-updates/