The ideal "reference" system would be that which is the most heard by the most recording engineers/people so that most everyone would have a common ground on which to base their opinions (i.e., a point of reference).
This is why I had previously alluded to the LS3/5As because most all British music is mixed, or at least sampled, over this set-up and most engineers would be familiar with the sound.
An American "reference" system would then include the likes of Altec 604s/JBL 4333s, at least for 60s/70s/80s music.
While not current state of the art, these were purchased from a recording studio and even at >45 years old this would qualify as a reference system.
https://youtu.be/iGa9259pz-I