I'm not sure if this was requested or if there is an option released recently (running on Beta 5). I think is important to have attachments enabled into conversations. Since we don't have a set of permissions that allow for Others' to view threads, I'm forced to use the Conversations as alternative. When I talk to clients, we both need to attach files and end up emailing them, instead of having everything grouped. Therefore, I suggest we add attachments to Conversations.