AO that would produce the results on both inverted and non-inverted normals, essentially meaning weathering + dirt. 
If possible, then why not?
I think the problem is that they react differently to spread and directionality, I found that in most cases you really need different values for each AO type. It’s only going to be useful and effective if each type gets separate controls.
Don’t think it would be very useful - weathering and dirt needs different maps/materials, hence separate masks is needed anyway.