I understand the difficulty with a 'texture' preview in a scene, but what about a basic "based on ideals" texure window, where for example the material 'aluminum' could be shown on a ball... insofar as to show us our choices for the available parameters against an idealized renderscene.
In other words, a modal dialog box that doesn't have any relation to the render conditions of a persons scene, but rather the way the materal is being rendered based on its' parameters.
In this manner we could see how much roughness we were to add and it's effect. How much density with a selected colour our glass would be.. etc. This kind of immediate feedback would reduce time doing 'test strips' by a factor of ten. If we could quickly go through all the metal and check how reflective, how much the color shows, etc.. It would actually improve our ability to render complex scenes with higher realism!
However, thank you for the technical explanation. Most developers don't respond in that manner assuming the users are incapable of appreciating the actual development issues you face. I can assure you this isn't the case and we very much appreciate the glimpse into your world.
Cheers