In order to maintain and upgrade legacy and hybrid contents, it is important to be able to determine whether a face has a PBR material applied. This is currently not possible unless the object owner has full perms -- a highly unlikely case for most products.
Whether this is done via a new flag for llGet/SetPrimitiveParams() or a new function is not important. But this functionality is urgently needed and will remain so for years, even after all viewers are PBR capable.
Please give this some priority, as it is essential for transitioning current products to PBR.