The Perfect Health Diet (perfecthealthdiet.com) advocates ~70% fat. The Optimal Diet recommends ~80% fat. PaNu for weight loss recommends ~80% fat as well, and for healthy people who don't need to lose weight the PaNu fat macro is still high at around ~65-75% (though he doesn't stress particular macro ratios, if you're doing it right, it'll come out to those percentages anyhow).
The only diets that are 90%+ fat are, as you've noted, therapeutic ketogenic diets and 'fat fasts' where consumption is completely fats, and in those cases it is a last resort. If you're not experiencing terrible suffering or life-threatening conditions then why would you event want to go above 80%? Perfecthealthdiet.com has a series on risks of prolonged diets without adequate starches/carbs, and PaNu has recently come out in favor of starches up to 20% (depending on activity level) as very healthy.
It is really easy to stay in the above recommended ranges--have your meals just be meat/fish/eggs with a side of veggies/tubers all drowned in butter/coconut oil. Very simple, very healthy, and best of all, very tasty!