Select material and cut-paste a new geometry
I would LOVE to be able to make a selection from a material's placement and then copy paste the geometry as a new object.
I happen to find that going from geometry to material back and forth is a bit tedious, So I'd rather "ungroup" my geometry and make it easier to change.
Having a right click option on a placed material to "make a selection from the material's placement" (= which means I already once on this project made that selection with the magic wand), or, second option "make a new object from the material's placement selection, and cut it from the object" (options : duplicate that part or cut/paste that part), would give me more time in creating than reselecting parts.
This should be very feasible. We do allow you (as of Dimension 2.2) to copy/paste selections of geometry into new objects. Right now the selection method is using Magic Wand, so if your material application is the same as a magic wand selection then you could do this today.
For a future enhancement we can add a way to select the polygons a material is assigned to.