So here are my guesses as October is winding down. I did say guesses
1. With the lack of rumours and or part leaks in 2018, it means Apple will more than likely retain the current form factor.
2. Should Apple pull a surprise bunny out of its hat and announce a redesigned iMac for its anniversary. I am calling a special November event for the iMac and Mac mini.
3. However my gut feeling is leaning on a silent refresh should Apple host a October event. With a redesigned iMac to be introduced alongside the Mac Pro and Mac Mini in 2019.
Either way I am not fussed given the rising cost of Apple gear, my late 2013 IMac is running even better now with Mojave. I can afford to wait out, rather than buy the same design again.