I’d love the ability to create custom chat commands in TS5. Yes, you can do this with a third-party bot but it’s not a great solution for the new TeamSpeak since global server chat is no longer a thing; this means you have to be in the same channel as the bot to use commands. I’m sure an official solution would offer much more power and flexibility anyway.
Edit: Not that I think of it, this is probably something that would have to be implemented on the server side. Feel free to move this topic to the server suggestions if needed.