Slack will never replace email
Slack also has other problems that have been totally ignored and neglected for years. One of them is accessibility. The app is impossible to work with without a mouse. They say it is "keyboard driven" and they keep adding features that ignore keyboard completely. Have you ever tried to jump to a thread without using the mouse? Or copy a link to the last message? Or share it? Or ask Slack to remind about it? Or snooze all notifications? They could at least put them in the main menu. People with disabilities who rely on things being in the menu, they can't do any those things. Can you imagine having to hire someone and they'd be like: "Ah sorry, I have to tell you something. I cannot use Slack app. I hope that's not a deal breaker". I wouldn't be surprised if someone sues SlackHQ for being discriminatory.