These quotes are so mentally defective that I have to ascribe them to bad faith. Wonder if the Heresy co-author would have the same view if it was decided that the Heresy never happened? Or Chaos isn't a thing. Of course it's fluff made to sell toys. That's no answer. It's just like any other fictional setting and set of characters created to sell toys, books, films &c. i.e. every work of fiction ever created in the history of humanity.
Thing is, every other sci-fi has a lore that has its own canon. Gundam 0083 Stardust Memory and Gundam 08th MS Team are part of the Universal Century Gundam canon. Dark Empire and Force Unleashed are part of the Legends/Star Wars Expanded Universe canon. Transformers War for Cybertron, Fall of Cybertron, and Transformers Prime are part of the Transformers Aligned Continuity. Star Fox 64, Adventures, and Assault are part of the Star Fox canon. Even media that has talking animals designed for kids to consume has a canon. Warhammer does not.
To answer your question, yes, they could decide one day that the Horus Heresy was just revisionist propaganda written by the Imperium or some other faction to justify something. Or that Chaos is just a part of something greater that is misunderstood. That is why 40K has no canon; they want to make retcons easy, and they don't like being held responsible to a canon. That's why the Female Custodes update doesn't really surprise me, since unlike every Youtube grifter who threw their two cents into the matter, who act like this change is akin to saying that Moses and Saint Paul from the Bible were women, I know for a fact that unlike the Bible and damn near every other sci-fi out there, Warhammer 40K has no canon for its lore, and GW openly stated it multiple times.
Canon and lore are just fancy words for the setting, the history. In modern terms, the IP. If you don't have coherent/consistent canon/lore you have nothing. More importantly you have no reason for customers to buy into the product if what you buy into today can cease to exist tomorrow.
The people who buy the actual minis don't give a flying shit about lore or canon. 40K lore has been retconned and upended multiple times; first during third edition, then during the Primaris update, now this. This isn't new. Seasoned 40K veterans who actually paint/assemble armies and play the game know for a fact that the lore is just fluff made to sell toys, and that it doesn't matter in the end. And the whales never cared about lore anyways; they just want to buy, paint, and play. The people who buy these minifigs in bulk are like those children who buy and play the Pokemon trading card game without knowing who the hell Ash Ketchum is, and why he has that Pikachu.
The division between the actual players of the game and the fans of the lore is well-established; it's up to the point where most of the serious lorefans for 40K out there have not played a game for over a decade.
Arch seems to be one some sort of press tour currently, first Craig from Sidescrollers, who is a complete waterhead who doesn't know a whole lot in general, and now yellowpiss. Endymion is another moron who jumped in on it, you can tell he doesn't know shit about 40k either.
For his supposed dislike of "tourists" in the hobby, he sure has been talking to them a lot during these last couple of days.
Again, it's good for clickbait and nerd rage, so of course these people would be talking to each other about the Warhammer Fem-Custodes debacle. Then they'll soon discover the truth when the next 40K box set sells out and scalpers start selling it at markup prices. These boycotts are about as useful as wet toilet paper.
