Are nukes on the table for Russia? Yes. Just like they’re on the table for us. Is it likely to escalate there? Almost certainly not. Many were surprised that we DIDN’T use nukes in Korea.
Maybe the talk about nukes dragged us in a different direction. The point is: if you argue that Russia is concerned about certain actions triggering escalation and assume they are actively managing those risks, you have to consider the increasing possibility of that mitigation failing at some point (human error) as the conflict drags on.
The USSR and US traded aircraft during the Cold War, sure. That was the norm. It is not the norm now, and retaliation in kind would be both justifiable and escalatory should that situation have ended differently.
Would it be WWIII? Probably not. Is there a series of unlikely, unavoidable events that would get us there? Yes.
The folks absolutely convinced that this is the road to the big one are probably nuts. But anybody whose job exists in the security apparatus has to consider it as part of the strategic context.