Real time chat environments are not conducive to long form communication. I've never been a part of an organization that does long form communication well on slack. You can call it a boundary issue - it doesn't really matter how you categorize the problem, it's definitely a change from email.
Regarding #4, I can't turn off my online/offline indicator, I can only go online or offline. I can't even set the time it takes to go idle. These are intentionally not configurable in slack. I have no desire to have a real time status indicator in the tool I use to communicate with coworkers.
- Long form discussion where people think before responding.
- Greater ability to filter/tag/prioritize incoming messages.
- Responses are usually expected within hours, not minutes.
- Email does not have a status indicator that broadcasts whether I am sitting at my desk at that particular moment to every coworker at my company.