IMHO the consensus is that a Japanese attack on the Soviet Pacific coast/Siberia is only feasible under certain conditions. Firstly Barbarossa is much more successful and you see the Germans taking Moscow in the late summer/early fall of 1941 possibly coupled with Stalin being killed and the USSR struggling internally for leadership. Secondly the USA along with the UK and Netherlands does not implement the full oil embargo in the summer 1941. The first because the IJA has recently been spanked by the Red Army and would not want to go at it again unless other circumstances have substantially weakened the Soviet military in the Far East. The second is because "it's the resources stupid" - to continue the war in China Japan needed the petroleum, rice, and more that SEA/DEI produced and in 1941 other than timber and some minerals, Siberia/Soviet Far East had none of these resources identified or exploited. No matter how badly the Germans are beating the Soviets, Japan cannot attack Russia without the resources it needs and it cannot attack Russia and the US/UK/Netherlands to seize resources simultaneously while pursuing the war in China. Only if there is total collapse and the IJA/IJN can march/land forces against essentially zero opposition can they have any hope of going north and south at the same time and even that requires a suspension of active campaigning in China.
The Germans would have dearly loved the Japanese to pile on when they started Barbarossa, every resource the Soviets would direct to fighting the Japanese is one less man/tank/bullet not being used against Barbarossa. Had Germany somehow been able to give the Japanese the oil (at a minimum) they so desperately needed this might have happened, but they could not do this. Theoretically had the Germans been able to force the Dutch to sell oil to Japan, or even provide it at below market rates or free as part of "reparations" after they occupied Holland this might have worked. Even with the Dutch royal family in exile, what would have been the reaction if the Germans had told the Dutch "sell/give oil to Japan or we will shoot 100 people a day (starting with the families of Dutch living overseas), and the number will increase if you continue noncompliance. If the US or the UK interferes with oil transport we will resume executions."
The problem with the Japanese attacking Russia AFTER PH/success in SEA/DEI is that they have basically committed all their resources, absent a Soviet collapse that allows them to walk in they simply don't have the forces to attack Russia. If they reduce the forces facing the US/UK their reteats start sooner.
