I don't know if it's still in the pipeline but I remember that Google proposed an "AMP for email" not so long ago, with basically self-updating email contents.
Open email can be severely damaged if good old SMTP is only used to tunnel proprietary formats, especially if those formats are effectively just metadata that's used to fetch the actual content of the email from 3rd parties.
[1] https://en.wikipedia.org/wiki/Transport_Neutral_Encapsulatio...
Most companies use mail internally or to interact with customers usually using some type of external mailing service.....
If SMTP is only used to tunnel proprietary content à la winmail.dat, it doesn't really matter that it's still technically open.
Isn't that what IRC was supposed to be? But as others have pointed out, it's trivial to roll your own chat software and monetize it. You can't do that with a decentralized standard.
slack/discord will probably disappear and be replaced by another closed system until we find the right way to do real time chat in a decentralised way.