The problem with "trying it with my team for one sprint" is that I now need to have a long conversation with legal. How will the service provider handle the content (discussions, screenshots, code snippets) that my team will upload? Do our current customer contracts contain any clauses that complicate the use of external discussion sites? In the unlikely event that the service offers the option to host it locally --…
Email isn't searchable by people who weren't on the threads. In an org that uses IM well (they exist!) the chat system actually becomes sort of like a wiki, except a lot more helpful.
That said, none of my employers have ever made effective use of this. I don't think open communication is an instinct that most people have.