(Campell Barton, I picked you since you are a modifiers module owner, I have no real idea who is best to review this)
I have put together a modifier implementing a deformation cleanup / relaxation method originally presented by Rhythm and Hues at siggraph 2014 (http://dl.acm.org/citation.cfm?id=2614144 if you have access behind the paywall, otherwise the video on http://www.fxguide.com/featured/voodoo-magic/ is a good overview).
The basic idea of this modifier is to smooth the mesh in a rest position, and record the changes in vertex position in each vertex's local tangent space.
After this, each evaluation of the modifier applies the same smoothing and then the original surface detail is reconstructed by re-applying these rest pose deltas in each vertex's tangent space. The effect of this is to smooth out deformations created by other modifiers etc (e.g. armature), while retaining fin surface detail.
For a comparison of the effect:
The modifier panel is based on the laplacian smoothing modifier (since it uses the same smoothing), and looks like:
Note that the UV map is for generating consistent tangents, as UV coordinates are required for tangent calculation.
I put this modifier together largely as a way of learning my way around parts of blender's codebase, so I sure there's plenty of stuff I could be doing more efficiently etc.
Regardless of whether this gets accepted or not I am interested in continuing get involved in blender, particularly around modifiers/deformation tools for character skinning.