Industry standard for material exchange format?

Do we have an industry standard for material exchange format yet? Which will be the better format to stick with? Preferrably an open standard instead of a proprietary one. I would like to now this because I would love to get into a more stardarized workflow with all Substance software on materials. Some popular formats in my research are:

• Appearance Exchange Format (AxF), from X-Rite (not an open standard)
• Unified 3D Material (U3D), from Vizoo
• Material Definition Language (MDL), from NVIDIA

I guess .sbsar is a good format but it's not open and it is focused no PRB textures only?