According to IGNs Endgame article the raids will be a 6 person team and there will not be matchmaking. They will be multi-hour experiences that you will fail repeatedly before beating.
I don't see why matchmaking would hurt the mode. But I also hope that means there are more 6 person fireteam content--explore at least. They should probably incorporate the clans more as well.
This also means I am going to need to bulk up my PS4 friends: SumJuGei or send me a pm and I'll add you.