There is a pretty huge problem with openGEX. Being a text format means its very slow to parse AND really big compared to binary files. Ive compared filesizes with fbx and its nowhere even near.
Some quick math: For your floats, it uses the hex value ex(0x3F800000). Thats 10 digits thing wastes 10 char bytes assuming 1 byte ASCII encoding for each character. That means that for lower precision(you would probably use way more digits) you are using more than twice the space as floats are 4 bytes normally. So its 10 bytes on text against 4 bytes on binary, and binary doesnt need parsing as you can just memcpy it while text has to be parsed wich is slower.
That doesnt happen on GLTF, becouse GLTF is a hybrid format, it has the scene description in text, but the actual raw data like the vertex arrays is done in binary format, wich makes it quite cool in my opinion. But that format is meant for WebGL and im not very sure how well it works as a exchange format, it has stuff like opengl state on it.
Blender .blend would be awesome, but reading/writing .blend files is specially hard given that .blend has pretty much no documentation and you need blender source to see it. Honestly, i dont know why there isnt a proper binary standard exchange format that works like FBX but opensource.