The Soviets would have to give up Kiev early on. The payback is that if they weather the storm it gives them something important to grab back before Germany is beaten. There’s certainly a stronger case for a starting factory here than, say, Stalingrad.
The problem with Vladivostok is that the map places it in Korea. Similarly Cape Town would be in the anomalous “South West Africa”, hence (I assume) the suggestion of JoBurg.
Addis Ababa is another possible for making Africa more valuable, and giving Italy something else to defend.
I also like Peking (a Soviet target in Japanese territory); Novosibirsk VC would be Chelyabinsk (the reverse).