use subdiv copy when baking displacement from multiresolution

Multiresolution is a great modifier, but it could be easier to bake out a displacement based on your sculpt. Right now the displacement is calculated between the geo in the modifiers "render" and the geo in the modifers "Preview". The resulting displacement when baking out with "bake from multires" is not compatible with a subdivided surface.

My suggestion is to make a temporary copy of the geo in the multires modifiers "preview" setting and subdivide it until it reaches the same polygon resoltion as the highest sculpted subdivision and then calculate the displacement between those two geometries (red arrow in image). The resulting displacement map would work very well with a subdivided surface later on.

My suggestion is to add a