"End Game" seems like a variable term defined by expectations. reaching expectations is the end.
so my 'end game' would be different than yours.
OTOH an 'ultimate system' might have certain commonalities, which i would agree include hearing the music and not gear or the room. that the music has flow and is lively, extended in the highs and lows, and has sufficient headroom to render large music naturally. and that it connects with the listener emotionally and is immersive and exciting.