I want to be able to send a "Reply" without having to receive an invite first.
I want to be able to reply to a reply.
I've seen some suggestions of an in-game messaging system, and I really think this is the way to do it.
Add a new button next to invite and request invite that says message. then allow people to use the system already in place for replies to send a message.
Allow people to reply to the message. allow people to reply to a reply.