I've seen https://developer.blender.org/T45473 where it's pointed out that if you have two quaternion rotation keyframes in Blender, it doesn't interp between them properly using slerp -- instead it seems to linearly interp each of w, x, y, and z, and then renormalize at each frame. This leads to very odd behavior when the keyframes are far apart rotationally.
The above-referenced ticket doesn't seem to have gotten any traction since 2015; I wonder if this has been fixed in the meantime, so there may now be a way in the API to specify slerp for quaternion interpolation?
I'm importing animations from another system, and they don't come out right because of this.
