Arbitrary Seams that are not Topological Edges

This would not be very compatible with other programs, but the pros are worth it:

Given a mesh with complex topology, you could 'draw' arbitrary seams on its surface using curves. The model could then be unwrapped according to this seam layout without affecting topology. The curves would always snap to the surface of the object.

Conceptually, it would be as if the model had a coating that was being cut up. It could have any number of these coatings.

The onus would still be on the artist to create a good map layout, but I dislike how you are currently stuck using topological edges for this (afaik). This overburdens topology with 2 roles; shape and mapping. Mapping is a shape-to-shape projection, there's no reason to be bound to the topological layout as I could just finalize then cut up the mesh itself arbitrarily; this would just be a nondestructive way of doing so.

There would need to be some serious thought to understand how these seams would deal with mesh changes. Likely magnetically linked to the nearest vertices or something.

EDIT

In this mode, you could also snap/trace the vertices/edges of the topology as desired.