The Russians claim they are opposing ISIL (or whatever we want to call them) but actually spend more energy attacking the other opposition to Assad.
The Turks claim they are opposing ISIL but have a different agenda: Support the Ethnic Turks in the border area, fight the Kurds, Assad and any Shia muslims who get involved. ISIL are Sunni fanatics (as are Al Q), Turkey is mostly Sunni.
I'd guess that the downed plane did not enter Turkish airspace, it was definitely bombing the ethnic Turks in the border area.
If Russia actually restricted their attacks to ISIL, Turkey would still be looking to attack the Kurds whenever they could.
The Russians only have one ally in the area - Assad. If they dropped him then they would lose face, other potential allies would not take them seriously.
The US are allied with Saudi Arabia and have been since Eisenhower. The Saudis have done very well out of this alliance, so have - to a certain extent - the US. The problem now is that the Al Q / ISIL strain of Sunni Islam is the Wahabi strain which comes straight from the Saudi ruling house - those two organisations are practicing what the Saudis preach. Acceptance of that conflict of interest would mean the end of the US / Saudi alliance. That would leave the US out on a limb - it would take a lot to get them together with Iran and that is the main regional alternative.