Along with "Join Fireteam" & "Invite to Fireteam" I have always wanted the option to click "Request to Join Fireteam". Instead of going through more trouble to send a message to a specific player that you want to potentially join. I feel a Request to Join Fireteam option simply makes it a little more convenient. We all like convenience. That's the basic idea. I'm sure there could be more structural soundness to it. For example, the potential receiving party could have the feature to disable the requests all together or have it open kind of like the normal Fireteam options (Public, Clan and Friends Only, Invite Only, Closed). Or on the receiving end of the request to simply click accept or deny. That way the person sending the request would know right off the answer, instead of waiting for a response. But regardless of that, the basic idea is a "Request to Join Fireteam" option.