If the iMac is to be a desktop high speed iPad Pro on a stick the environmental argument seems a little weaker. Mac mini units are huge compared to their contents.I don’t understand the fascination with an all in one desktop. Apart from being super cool, wouldn’t it be better to have a best in class apple monitor and the computer unit separate. I can change/upgrade either one as required. If space clutter is a problem you could always create neat ways of hanging a Mac mini on the back of the monitor. There is so much waste at the end of life of an iMac. It’s a shame that Apple can shout from the top of solar roof tops but not care about the environment for real.
Also iMacs last ten years minimum, that’s not a bad innings for a monitor these days.