Considering that Russia explicitly drew their line in the sand to the west of the Euphrates (assuming they follow through) and the vast majority of SDF territory is to the east of that line, they might be tacitly accepting the existence of a US backed semiautonomous state once ISIS is out of the picture. An important factor is that up until recently the Kurds were more or less a third party primarily concerned with Al-Nusra and eventually ISIS. They’ve had truces and worked with the SAA before, and possibly had contact with the Russian military as a result. Of course now that’s 180'd to the point that you have Russian media making the claim that the Kurds are equally as bad as ISIS, but that doesn’t mean Assad will be treating the SDF with the same amount of animosity he treats the FSA during the ceasefire talks. Especially since the US is more overtly supportive.
Whatever the case is this issue is not going to be resolved at any point in the near future. My own prediction is that after the civil war “ends” the Kurdish-controlled region of Syria will become a pro-Western equivalent of satellite states like Transinistria, South Ossetia/Abkhazia, and the DPR. The Syrian government will officially claim sovereignty over the region but the reality on the ground is that it’s an independent Kurdish state in all but name. Neither the Syrian government will try to crack down on the local government nor will the Kurds go all the way in declaring independence. If either faction does so that means they risk drawing the ire and military response of the power that is backing their enemy. Instead the dispute will be in an indefinite political limbo until both sides somehow reach a compromise or either Russia or the USA completely drop their support of the faction they’re backing.