"E2EE" is not really basic functionality.

I believe it is hard to get right, and only worthwhile on 1:1 communication, it doesn't work well at all on large chat rooms, which is what IRC is.

Regardless, if you don't want E2EE to be handled by a plugin- it is possible to make a client with it baked in.

There is no company that will stop you creating a third-party client unlike slack/discord which are extremely hostile to those endeavors by comparison.

EDIT: If you downvote without replying I'm just going to assume you're ideologically opposed to open standards, because I'm not sure what else I can take from it.