Played a solo Soviet run at veteran difficulty, and japan had some issues:
1. Japan did nothing after Siberian troops removed 100%, there should be some limit for this action against the AI. Simple solution would be stoppi9ng the Vladivostok route if no units near the Japan-SU border, trickier would be a chance that the Japan AI DOW on SU or some event that takes the border territories or something.
2. Liberation of China. After Peking got liberated, China moved its capital there, and the SU supply went from good to terribly, since no cooperation between China and SU, which is alright in most case, but in this case, CHina got completely occupied and surrendered, they might want the Soviets help, and not stop the liberation of their country with limiting the supply. Not sure how could this be done, but it was really annoying, maybe an option for the Soviet player to not liberate China, but occupy it for the Soviets or the Communist China, that turned over the Soviets.
3. Similar suply issues in the Japanese landings. A Single US unit managed to land after the Soviets already landed in northern Japan, but the small territories and the no cooperation meant, that the landed unit (an HQ) just took over the hex and limited the supplies for the soviet troops, and did nothing useful. While could disband and "retake" the control of the hex from the US to SU, it was interesting to got worse position by friendly landing. Not sure how could this be solved, if anything needs to be solved, maybe it is just the preparation for the post war conflict.