My opinion is that it should be required. I think if it is optional then the backwards-compatibility of using names later on is as difficult as if names were not an attribute in the first place.

I do agree that the user shouldn't need to type it; I don't think the user should even need to create the VisualizaitonFrame's on their own. This gets back to the discussion of the scene automatically generating a VFrame for each rigid body given to the scene; in this case, the Scene could automatically take care of naming the VFrame's according to its rigid body.

I don't think it's the end of the world though if names are not included. One option is, if the name is omitted, to set the VFrame's name to that of its rigid body.