Not sure what the X/Y problem is, could you elaborate on that? I'm curious. I don't have any VSL instruments yet other then the stuff that came with VEP. I'm assuming you're dealing with something related to the VSL xy matrix.
So anyway Logic pro can support up to 254 articulations per articulation set...meaning you could have as many as 254 articulation id's on a single track. Where are you getting the limitation of 127?
I agree with you that Logic may never adopt AU3. Well maybe someday, but probably years away.