Proposed by MickP in this thread: https://sourceforge.net/projects/assimp/forums/forum/817653/topic/3700488
There should be an additional post processing step to join adjacent coplanar triangles to polygons. Possibly convex polygons, only, and definitely only when bordering vertex attributes match.
Lowest priority because almost all users request triangulation anyways. Polygons have undesirable properties which make them useless for most applications.