Obama lies, he will make sure US "advisers" have the ability to down Russian aircraft.
The Russians will target ISIS and US backed terrorist "rebels".
A US "adviser" will take out a Russian aircraft, Russia will shift targets, and attack with ferocity, and target any aircraft that responds to aid or extract said "advisers".
It will be on, and the Russians will not back down, as their gear has been working well so far.
Sounds rational to me. I agree with your thoughts.
It could get funky, real quick.