i suppose this is why macs (according to consumer reports) are 1/3 less likely to fail in their first year and over three years are half as likely to fail as their windows counterpart? so they get hot under a heavy load. the fans ramp up and they cool down. the current imac is fantastic and there is no windows machine that comes close imho. there is no evidence that these have design flaws that will shorten their life. not to say apple doesn't make mistakes, they've made plenty. but this, so far, knock wood, doesn't seem to be one of them.
I have two friends who's first gen 5k fried itself. Both editors.
There are several repair men on this forum who will gladly tell you about the rise of heat related failures they have seen with the past two models. Running a GPU / CPU for hours a day at 80-100 C is not a good idea no matter how you cut it. Sorry, that's just physics and has nothing to do with opinion.
Do a google or youtube search about iMac 5k heat issues. It's a much discussed topic in the content creation business. Nice machines, but unfortunately crippled by bad design decisions. With Jobs gone the only person at Apple who has the authority to overrule a design decision by Ive is Tim Cook and that would only happen if a product literally crashed and burned. Heat is a problem for anyone pushing these machines heavily on a consistent basis, especially if you live in a warmer climate. The Skylake iMac is an improvement, but under load it runs just below the thermal limit and considerably hotter than the Mac Pro. And you'll have to listen to the fan blowing on your keyboard.
Believe me I take no pleasure in the current situation. I've used Apple machines since the days of the Apple II and the Fat Mac. If I purchased an iMac the first thing In would do is drill a large ventilation hole in the back and maybe even add a small exhaust fan. That would probably eliminate any heat related issues. Not pretty, but better than frying a machine.