I don't mean remove them by the way. Just make them dead in-lore, but playable in-game. Not everybody has to be invincible, and it opens new opportunities for new skins.
Once the bio updates are done, I'd like to see the league's universe move forwards into an actual lengthy story.
I know there are several Warhammer writers on the lore team, so why not do something similar to the Horus Heresy. I.E., books set in the same universe with a similar overarching event, but separate stories that tie into each-other somewhat.