This does seem a nice feature and definitely a step in the right direction but why use e2ee for video and audio but not chat? That's afterall where most of Discords activity is happening
Because E2EE causes an absolute ton of friction to the chat experience. Stuff that you expect to just work like chat history and searching no longer works.
Haven't used WhatsApp but presumably it indexes client-side. On Discord people want to search large servers including messages since before they joined, so this approach wouldn't really work.