The way it is now, reading the PBR properties of a face using llGetPrimitiveParams() with the PRIM_GLTF_X flags will only return parameters that are overrides of the underlying material asset. In other words, it is impossible to read all PBR texture parameters via scripts. This is a severe restriction, and one that appears to be more severe than what applies to Blinn-Phong textures.
Being able to get and set all texture parameters is very useful in a number of contexts. This is unfortunately made very difficult if not impossible in the current model.
We need way of accessing all parameters of PBR materials applied to a surface, not just the overrides. While it may be necessary to impose permission-based limitations, at a minimum it should be possible to do this on objects that the user has modify permissions on.
PS: It's not always obvious what constitutes an "override." For example, all that is needed to create an override of the Tint parameter is to click the color swatch and then immediately close the color selection dialog without clicking a color -- any color, even the currently selected one. The tint clearly doesn't change, yet the parameter is now an override.