Looking over the PH I can't help but compare 5E to other d20 derived games.
I think that 5E might be the first d20 derived game since True20 that I feel comfortable using the take ten rule.
I always found scaling DCs based on the characters level and skill points made taking 10 only useful at very low levels. With 5E a DC 15 task will always be a DC15 task. And not a DC 20 just because the character is over level 15.
I've never really like the idea of Take 20, The idea with more time and no stress you are able to not just work more efficient, but at your 100% best every time you do it. Although it does make me thing a Take 15 rule might just need some play testing.