I don’t associate it with WASP’s. Possibly more WASP’s are likely to be names after their father, and so they are then called by their middle name to not get confused? Dropping the first name to an initial would create less confusion when people see the name I guess? Otherwise people immediately assume to call someone by their first name. I don’t really know, just hypothesizing how the practice might have evolved. Traditionaly Ashkenazi Jews (most Jews in America are Ashkenazi) don’t name a child after a parent, so that would not be a problem. However, my grandfather went by his middle name, which I am not sure if he was gven it at birth, or took it on in America. Anyway, WASP does not jump into my mind when I see a name written that way. When I see a Jr or III I tend to assume not Jewish, but that is about it. My husband is named after his father, but does not use Jr.
My husband finds it odd that so many Americans go by their middle name, but that is aside from the first initial full middle name thing. He was not given a middle name, and finds that practice a little strange anyway. In his culture you are given two last names, your dads followed by your moms.