I give this 0% chance of spreading into NATO. Ukraine is easy pickings, NATO not so much. After Ukraine I could foresee moves toward the Baltic nations at the very most in the distant future.
In one way I'm glad my father isn't alive to see what's going on In Ukraine. He was a refuge who fled from the Russians in January of 1945 in Poland. He lived close to a sub-camp of Auchwitz and saw prisoners in a forced march. They fled Poland with the retreating German Army into Checkoslovakia and then into war ravaged Germany.
Invading Kiev might prove costly if it comes down to street fighting. The Soviets had a bloody time taking Berlin In April of 1945. Not just fighting house to house, but floor by floor and even room by room.
I'm not saying that will happen.