There was a Saturnine Gate in the old bill king story. Which was the outer gate theyve been fighting over so far. Cant remember if it was called that in universe.
The series so far seems to vaguely mirror the events of the story.
Which is about where we are after Khan retakes Lions Gate. Dunno if hack thorpe mentions the eternity wall port.
So at a guess.
Saturnine is the Deaths Heads rolling in and smashing up the place. Kind of appropriate, given its Abnett.
The fight for the inner palace. The BA will probably be firemen, rushing from one fight to the next.
The retreat to the inner palace and Sanguinius holding a gate again because GW like telling the same tale 2 or 3 times.
Where he duffs up KaBanda again.
I wonder how accurate that will be.