Sure. I looked at this in the past (hacking it in to see what kind of an effect it would have) and it wasn't very impressive, even on my more aggressive hikes/rides.
Perhaps I need to start recreating more agressively!
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I think it should probably be on the main stats screen - terrain distance.
At a 30 degree slope (which is steeper than 30%) you gain 15% more distance than straight line. Even if there are extended sections, most of the route is not going to be near that.
I found that even on long, aggressive rides (say, 60 miles and eight to nine thousand feet of climbing) it only added a mile or so. But, I still think it should be added.
Thanks for the suggestion.