Related to this thread I have been working for a while now on an upcomming tool for TexTools called “Pin & Relax”
It unfolds and Pins selected edge loops into straight lines and relaxes the rest of the UV island. Similar to Headus UV layout with its edge constraints. Unlike the previous examples here it does not re-scale the edge distance but instead maintains it.
There is also support for selected multiple edge loop sets where it straightens and relaxes them largest to smallest but this mode is not yet fully fool proof.