Just some thoughts about the current state and possible developments, I had little time to check much what happened in the meantime.
I think it is well known how stretched the SAA has been in the last years and it's increasing reliance on a restricted number of actually Syrian units capable of offensive action.The loss of Palmyra was an good example of what could happen if the leadership shifted the limited amount of decently well organized, trained and led troops with it's supporting assets to another are of operation. A fairly low quality melange of shifted local militias, third-tier elements with some decent assets were quickly overrun by a rapid and aggressive IS counter-offensive with had mobilized with speed and skill.
With a decreased availability of Hezbollah and "Iranian" (partly Afghan) boots on the ground the regime had to chose it's strategic targets and where to concentrate forces with care. Perhaps more importantly it had to balance to which degree it could strip more tranquil areas of manpower. Offensives have been pushed forward leaning heavily on firepower and air support organized and executed to a large degree through Russian assets and personnel. The model is actually roughly comparable to the way ISIS was pushed back in Iraq and Syria with Western support. There are also some parallels to the German way to help the Franco coup in Spain, bringing in air mobility, air power, firepower, planning and communications.
As things are happening fast and a large part of the better Syrian units have been concentrated against Idlib and not too far away from the SDF-held areas west of the Euphrates I suspect that some serious fighting power could be shifted into said areas. East of it the central northern area will see at first mostly lower class light infantry quickly motored and perhaps airlifted towards the Turkish pushes. Movement on the streets will be hampered by the tens of thousands of fleeing civilians. Russian presence in the air will be important to monitor the situation, including the traffic and to deter attacks against said movements. Don't know how well it will play out.
What we can expect in all areas imperiled by the advances is a switch of patches and flags, with the Syrian national flag popping up all over. I would not be surprised if the troops bussed in are bringing a large number of them, perhaps with some Russian ones as well. As said before first the PKK transformed partly into the YPG, then the YPG was augmented and developed into the SDF and now we have the SDF shifting to some degree into the SAA. Especially in the East the boots of the SAA will be for the time being be the old SDF.
While Turkey and Russia will have some high-level talks the rapid developments on the ground, the tendency of operational success leading strategic considerations, the use of militias and not closely integrated groups, some resulting plausible deniability, the transformation of the SDF and the general confusion will leave plenty of scope for clashes on the ground if military history is any guide...
