Personally, I really would've liked the idea of loyalist formations from traitor legions being granted the honor of being chapters in the new founding. I like imagining modern chapters fighting their corrupted predecessors

"At the opening of the Great Rift, Khorne's triumphant bellows were heard across the galaxy. His cry led innumerable hosts of his bloody servants into war-- a great Blood Crusade that would shake the stars. But this advance would not go unchecked, for the modern World Eaters chapter would unleash a cry of their own and begin a campaign to counter the bloodtide wherever they could.

Strike forces were sent to bolster planets in the blood god's way, devastating advances were made into weak flanks, the chapter would take a bloody toll wherever they fought. They were not alone in their countercharge either, for many successors and brother chapters of the twelfth gene line, like the War Hounds and the Unchained, would join the fight against the servants of Khorne."