This feels like the sort of thing that could be easily solved with technology. Something like: if I receive a message on slack with the message hi, how are you, hello, or something similar, wait 15 minutes to notify me about it. For all other messages, notify me as normal.
It's a social issue, not a technological one. People just need to be ok communicating with people who have different styles. Most people do not care to optimize their communication like this and will have a more natural way of speaking, including starting a conversation with "hi".
None of that is how communication works. It requires (basically equal) effort on the part of the sender and the receiver. Gatekeeping communication styles is just a symptom of not having control in other areas.
If people are annoyed by someone saying "hi" then yes, I think they are in the wrong and creating a hostile work environment. I've worked on a lot of different teams, and people who complain about stuff like this are always the single biggest drag on morale. Teams should practice tolerance, trust and flexibility, especially remote teams.
