I think a possibility that hasn't been brought up is that the Soviets might end up making a landgrab in Manchuria. The Russians and Chinese had been enemies for centuries. In our TL, the USSR and China weren't on friendly terms from the early 60s on, the tensions escalating into a limitied border conflict in 1969. Russia in late 1950 doesn't have much capacity for force projection. It's a country still reeling from the devastation of WWII, and the Red Army in the last war rolled on American trucks and filled its belly with American food supplies. It isn't going to attack the West, but maybe it sits back for awhile, lets the UN forces do the dirty work, then swoops down on the battered Chinese like a vulture to pick off some meat? Stalin was a pretty kooky bird, himself, and I wouldn't put anything past him...