Could the treaty exclude Japan and give Imperial Russia Japan's place?
Short answerNo practical settlement could ignore Japan, because an unrestricted Japanese navy would keep building while Britain and America were constrained.
NotesBritain and the United States cared more about constraining Japan than about limiting the relatively weak Russian dreadnought force. Japanese ships, crews, and construction plans already posed a serious Pacific challenge. If Japan withdrew while Britain and America remained bound, Tokyo could continue building without restraint. The Western powers would then abandon the limits as well, causing the entire agreement to collapse. Giving Russia Japan's place therefore solves the wrong problem.