Naturally I would love to see the KV-1 & Tiger included, but I'm thinking it would be a little more realistic and fair if we saw the KV-1 first and then got the Tiger later. Reason for this being ofcourse that the Germans initially had a really tough time with the KV-1 because of its thick armour, and second because once the Germans got the Tiger they had a tank with litterally no equal for the next 2 years of the war.
I'm fearing that once the Tiger enters the game we will see a lot of complaining on these forums, seeing as the Soviets had no tank armed with a gun capable of dealing with the Tigers frontal armour until the 85mm armed T-34's & KV85's, and even then it was at close range. The 76mm F34 was hopelessly inadequate against even the side & rear protection on the Tiger, where only the Zis-2 stood a moderate chance of penetrating at close range.
By contrast the Tiger's 88mm KwK36 would punch a hole in a T-34's glacis plate from over 2km away, and the KV-1 wasn't safe at that range either.
In short, adding the Tiger to the game would be great and naturally has to be done at some point, but availability has to be kept low, just as it was in reality.