Blend shapes or lines along a curved path, like a "spline".
Type can be arranged along a custom curved path. Why not blends? As it is now, if I want to arrange repeating vertical lines along a curved horizontal path, I have to: create the blend in a straight line, then: line by line, go along the blend cutting off bits to match the curved horizontal baseline. I can make it look decent, but it takes quite a while.
As per the comment, you can replace the spline in a blend via Object > Blend > Replace Spline, if you have a blend and a new spline path selected together.
Looks like I missed the boat on this one. I have made that feature request every few years since about 1998, and then never checked the " New Features" to find out if there were any changes in blending. Thank you, Wes Rand, for drawing my attention to the feature, and thank you, Adobe, for incorporating it. I guess this thread can be marked "inappropriate".
Wes Rand commented
You can replace the spline in a blend with a curved line. Having more control over the rotation along the line would be a welcome feature.