I think from what we set forth in the IFC4 certification, transparency IS expected to be universally supported, but textures were out of scope. I know GRAPHISOFT had been pushing for universal support for textures for some time, but it seemed low priority for almost everyone else. My reaction was to set up a Task Force/Working Group to figure it out and move things forward.
I think it would make for a good, formal, technical project for the vendors to cooperate on support, first examining if everything that is needed to properly and effectively do it is actually in the schema, and the best way of doing it. I’ve heard whispers that it is suboptimal, at this time. Then, I think there needs to be consensus by users on the best way to use it, through either an “add-on” to an existing MVD or a new MVD. If you want an international standard MVD, then the procedure is to create project around it.
I know @Moult has started topic threads to address this for the future:
IFC Textures and Colors: Current Situation - Developers - buildingSMART Forums
Textures and Colors: Criticisms and Issues - Developers - buildingSMART Forums
Further searching on this Forum includes:
IFC - Problem about Elements with Texture - Developers - buildingSMART Forums