I think Mono-Legion books are a thing that also doesn't suit the narrative anymore. The late Great Crusade and early Heresy allowed for it to great extent, but now? Everything is being funnelled to the Siege. It is inevitable that storylines converge the closer we get to the finish line. You can't really tell something like Legion or even A Thousand Sons anymore (though even that shared some screentime with the Wolves, for obvious reasons, despite its primary focus on Thousand Sons). Most forces are converging around the center of the Imperium. The theater of war has shrunken to center of human civilization, and they're going to be bumping heads.
And again, we've had indications that the Death Guard's story is intertwined with that of the Grey Knights founders for years, including Mortarion's Heart and Pandorax. Their part isn't big for the Heresy itself, but a bunch of their post-Heresy role is rooted directly in the Heresy, including the stuff on Pythos with the Damnation Cache, where a Death Guard daemon prince will be involved at the closing of the rift.
Frankly, I'm not enthusiastic about Swallow writing this. Wraight would have been my preference. But by the Emperor, that degree of incessant whining about how a plotline we haven't experienced yet supposedly ruins the main narrative weeks before we get to read the book is just silly. We can complain and critique later when we've actually had the book in hands, but right now, you're complaining based on conjecture, based on a dramatis personae, which often list characters with barely any role whatsoever or even to somehow "wow" the reader going in.
Edited by DarkChaplain, 09 February 2019 - 08:46 PM.