You're probably quite right there, Nev. We might have only seen the tip of it.
This is the Eastern Gulf region as I see it:
All America's loyal allies (excluding Israel) in the region are Sunni.
IS is Sunni
Iran is Shiite
The minority Iraqi government is Shiite
Assad's Syria is Shiite related
Russia's main influence in the region is Iran and Syria which they would like to maintain, and possibly increase to other countries.
Iran, for it's own security, would like to maintain influence in Syria and extend that to Iraq. The previous Iraqi leadership was getting very friendly with Iran and Russia, then all of a sudden, IS showed up. Goodbye Iraqi leader, hello new approved guy.
America would like to extend it's influence to the entire region. Iran is in the too hard basket for the US, but they would like to control Iraq and Syria to contain Iranian and Russian influence.
Sunni Gulf States would like to see Syria as a Sunni state, to enable oil to be pipelined via Syria to Turkey.
But I could just go on and on, there's no end to it, just one big chess game. Unfortunately for Syria, they're just a pawn in all this. There's talk (probably just a conspiracy theory) about a looming US/Russian deal. You give up Assad, we give you the Donbass.
Back to aviation - Syria received six MiG-31 interceptors from Russia a few days ago, after the US descision to invade Syria's border with air strikes. Maybe a little message there from President Putin - bomb IS, but stay away from Syrian Government forces. I think the MiG's are upgraded to a reasonably capable level.
To quote Jane's on the Syrian MiG-31's:
"In particular, the MiG-31's NIIP N007 S-800 SBI-16 (RP-31) Zaslon or Zaslon-A electronically scanned phased-array fire-control radar (NATO codename 'Flash Dance') affords it an impressive beyond-visual range capability, enabling it to see airborne targets out to a range of 108 n miles (200 km; 124 miles) in a clutter-free forward sector, or 48 n miles (90 km; 56 miles) to the rear. It is capable of tracking 10 targets and attacking four simultaneously. Coupled with this radar, the MiG-31's R-33 (NATO codename AA-9 'Amos') or R-37 (AA-X-13/AA-13 'Arrow') long-range air-to-air missiles afford it a highly potent beyond-visual range (BVR) air-to-air capability."
Syria sounds like a good place for us to stay out of.