"Russia appears to have begun a significant, direct military intervention in Syria. Extensive reporting, including some attributed to U.S. government and intelligence sources, indicates that Russia is building a joint air-ground expeditionary force in Latakia and Tartus provinces along the northwestern coast, far surpassing the scope of its longstanding advisory and arms-supply role. If this force develops along the reported lines, it could be a game-changer in the war. It could also have major implications for Israel's ability to conduct air operations over western Syria and Lebanon, and for U.S./coalition operations against the "Islamic State"/ISIS and other terrorist organizations in Syria.
Moreover, if the Russian presence becomes established, it will be increasingly difficult to remove. As in Crimea and Ukraine, the United States -- much less any other country -- seems unlikely to challenge Russian forces militarily. And while these forces will probably suffer casualties and could become bogged down in Syria, Moscow may well accept that as the cost of keeping the Assad regime in power and frustrating Washington." Jeff White at WINEP
Well, Jeff, better late than never.
"... and for U.S./coalition operations against the "Islamic State"/ISIS and other terrorist organizations in Syria."
Oh, come on - all that would be needed would be a small de-confliction cell somewhere to sort out air space use and missions.
How that would work for the Israelis is anybody's guess if potential air combat would be in an air space covered by Russian air defense units.