BBC is a pretty reliable source.
At the end of the story, they bring this around to the supply lines between the ISIS capital of Raqqa, and the major city of Homs.
The gist is that the Syrian Army, backed up by the Russians and Iranians, has been having a bit more of a fight from ISIS than hoped - and that ISIS supply line remains open.
This may effect the operation that just launched against Raqqa from the North by the Kurds/SDF, perhaps slowing the timeline somewhat. Perhaps the Kurds/SDF will just draw up close to the city, dig in a half cordon and hold, until conditions are set (or until they get a better deal on Manbij/Jarabulus).
We will see when the air attacks pick up in earnest on Raqqa.
Raqqa’s three main supply lines are SW across the center toward Homs, West toward Turkey and Aleppo (past Tabaqa Air Base), or SE down the river toward Dier ez Zour.
It looks to me like Syrian/Russian priority of fire is going to the battle around Aleppo city, rather than isolating Raqqa - looks like that is being left mostly to Americans, if they will step up to do it.
Again, if we see significant air assets hitting ISIS around Raqqa, that would be perhaps the best indicator that it is showtime for clearing ISIS from Raqqa.
My guess is that the external players will continue to drag out the end game while trying to improve their positions, but that the US will seek some high profile victories over ISIS, for political purposes in an election year. Raqqa could go down anytime the US supplies the money, weapons, ammo and air strikes to do it. It certainly seems like that day is approaching, well before the election.
The ISIS caliphate could just collapse at any point from the combined pressures they are under, and convert to a terrorist franchise, but the Saudis and Turks will probably try to keep the dream alive with money and weapons...