How Feasible is this plan?
Germany's poor treatment of Jews and Poles would already imperil their relationships with minorities in the Soviet Union.
This is very far from a knockout punch against the Soviet Union. The Balts and the Ukrainians might support Germany, as might a few of the less numerous peoples of the Caucasus.
I have little doubt that the Germans could have done much better if they had acted against the Soviets in this fashion. But actually taking down the Soviet Union itself is still going to be a formidable task--not helped by the fact that the Russians would have withdrawn their industry into the Urals and are going to be fighting against an attempt to destroy their people.
The Soviets probably still carry the day, but its a harder, longer war, with the Germans making heavy usage of OstTruppen against the Soviets. The Problem is that even if Germany builds a strong defensive line in the Soviet Union, the Western Allies are eventually going to Nuke Germany. D Day III is going to sink Germany, even if the Allies have to drop 30 atomic weapons to do it. In the end, a German stalemate heavily favors the Allies. And its hard to see much more than that happening. The Soviets are going to stop the German advance, be it at the Gates of Moscow, at the Volga, or even at the Urals themselves.