What about a brave suggestion to make all work chat communication public to all employees. This would allow you to just randomly come across interesting conversations (tags, keywords, etc..) your coworkers have without inviting you. If on the other hand someone wants their communication explicitly private, there could be a toggle in chat app to enable that. Like you don't discuss sensitive topics near the coffee machine and just move to a meeting room.
No this is a terrible idea. Spoken conversations are different to chats. For one the very fact that they're not searchable after the fact makes everyone more relaxed and not worry so much about saying something wrong that could get back to them later.
For another, spoken conversations are ephemeral but also point in time. Archived chats need to then be cross-referenced with time and date to check if those chats are still relevant. If partially relevant, which parts can or must be excised?
So public by default, private by choice.