Well, to me, its as vague as succeed and fail are - they get about the same.Sure, it's discussed as a possibility. But it's pretty vague is what I'm saying. One of the things I like about 5E is that they seem to have left it very malleable so that different groups can use it for different styles of play, and could tweak it as needed. The DMG is largely a list of suggestions on how to do so.
And that's great. I don't know if I'd hold it in the same category as a game that includes partial success in a more definitive way. As we've seen in some discussions on the boards, the very idea isn't always easily understood, so without actual rules, it's harder to grasp. For those familiar with the concept, or who take the mention in the PHB and DMG and run with it, yes, you can establish a pretty different system. But I don't know if many people would do so.
I mean, if i am climbing a treacherous hillside do i fall on a fail or just get bo ehere? If i succeed is ot one check for the whole climb or one per my half speed climb segment?
Basically, i do not see the progress with setback as any less detailed than the other two options - each is left to the gm to define based on circumstance in the PHB ability score.