retopologize based on a texture? I can subdivide a mesh, for example a coin, many times, then add a texture to it as a Displacement modifier to add detail on the mesh (coin), for example a bust of a famous person.
However, the displacement modifier will require a lot of polygons (over few millions) to make the relief look smooth and detailed. A lot of those polygons are useless and piece in a large group of planar polygons. The 3D preview can also get hard to navigate with the CPU/GPU reaching their limit.

A more practical and easier approach in my opinion would be to have the topology regenerated based on the texture used for the displacement modifier, then adding polygons to that mesh instead.

Is something like that possible?
As far as i know, it is not possible, you have to do a manual retopo or use a decimate modifier to reduce the polycount.