I know the Russians would have done anything to get a toehold on Hokkaido and/or northern Honshu to get a piece of the action in post-war Japan. You know they would not have cared about their own losses, or losses among the Japanese population. The Russians have generally looked down on their Asian neighbors as “little yellow sub-humans.”
They didn’t have much sealift, but on the other hand, could the Japanese have done much about it? I’m assuming the Russians would have attempted their landings after the Japanese had expended most of their kamikaze planes in Ketsu-Go.
From the description of the ships transferred and the problems they had on Sakhalin, however, these ships could not transport high volumes of troops and could not transport armor or artillery. I doubt they could have landed an army big enough to swallow Hokkaido, even at that late stage of the war. Even if they could, it's probably not enough shipping to keep an army of any size supplied with ammo and food.
Amphibious warfare and supplying an army across the sea were not in the Red Army's wheelhouse. They had real trouble with the little garrison on Sakhalin. So, I now doubt they could have pulled off Hokkaido.