They should add in hubs to the tower and the reef in which a player can go up to, access it and add themselves to a public matchmaking list. All you would have to do is set your criteria, Raid -> Crota -> hard ->"add to list" Now fireteams would go to the tower, check the hub, set their criteria and it would show all potential fireteam members that matched the search. Fireteams would then be given the option to inspect and invite players from the results. Once a player is chosen they are removed from the hub. I realise this would be slightly pointless mid activity, but it beats getting a team together via bnet pre activity