If it were a Russian fighter, it wouldn't have happened in the first place -- not only are there presumable ways to identify what country a plane is from, of course, but evidently we were in contact with the Russians over a special channel.
Yeah, and it didn't stop the bombing attempt. Also didn't stop the cyber attacks, for that matter. I wouldn't put much stock in special channels with russia doing fuck all, at this point. Maybe russia wouldn't bomb american forces (intentionally, or at least "intentionally"), but the plane that was shot down wasn't attempting to, either.
So far as nukes go, war's pretty unlikely still, sure. Unfortunately, on the nuclear front it's not really
war we're notably worried about, but escalation and brinkmanship. What's more on the table than it should be is seeing is deployment of tactical scale (i.e. the tiny tiny ones, as nukes go) nuclear munitions.
That is what putin has been intimating as being willing to do, and it's
also something the current US majority party (and yes, including the current POTUS) has stumped for or refused to categorically state was off the table. War might not be a possibility, but the worry that's worryingly legitimate is this shit bringing nuclear arms to the battle field, if not strategic theater.
... all that said, is this event marks the beginning of a no-fly zone functional or explicit, I am going laugh, and laugh, and laugh, and laugh. And then maybe cry or throw things at people, I'unno.