People are still writing clients without tls support. Why would you think e2e support will have better adaptability? People will move away from it when they get enough number of messages that require turning it off because the other party does not support it. Nobody wants to join your channel because you need them to have one of a few clients in a very short list in order to join.

We already have OTR (for quite some time now) and matrix has libolm - things aren't and won't change because the best you can practically implement it is using opportunistic negotiation and that is bad security. Best case scenario(imo),20 years from now 95%+ of irc users will use e2e. That is unacceptable when we already have fully e2e chat today. Let's break compatibility and have a separate network for the new secure protocol. At least that way people that move over don't have to look back. When foss projects move to the new network everything else (again,pure opinion) will follow.