I am wondering if you will be allowing this to be public knowledge before your drivers are released to support this. I will be implementing a feature in the future that uses image units for on the fly GPU texture decoding, and implementing it in compute shaders or fragment shaders depends on if image units are exposed in fragment shaders.
According to the OpenGL ES 3.1 spec, the minimum amount of image units that the spec requires to be conformant is 4 units. These 4 units are only required to be in the compute shaders, the minimum maximum(GL_MAX_FRAGMENT_IMAGE_UNIFORMS page 395 of the GLES 3.1 spec) specifies that one can have 0 image uniforms available to the fragment shader to be standards compliant with OpenGL ES 3.1.
Will you be exposing image units to the fragment/vertex shaders in order for one to do image load/store operations in these shader types?
I think for now I'll have to take Qualcomm's line and say we don't have anything public in relation to this at the moment... But again, it's spec guaranteed you'll have 4 in the compute shaders. You might have to compromise slightly and go for compute shaders on ES 3.1, fragment on desktop, or require the compute shader extension on desktop, and go pure compute shader. Actually, as you already have an SSE fast path for x86, maybe it's ok to use compute everywhere if it's available, including desktop, and ignore the fragment option?
Hth,
Chris