I believe in the buddy system. It's only manageable to keep track of 1-2 people at a time. A crew should be 2-3 people. If 7 people are riding together, then it's 2 crews of 3, and 1 crew of 2. Larger crews can more easily lose people. I haven't discussed this with the people I ride with, they may feel differently about it, but I usually stick with the person I go out with. I may go ride with 6 or 7 people, but if I go out with Tom, I stay with Tom, and I return with Tom. I only seperate from Tom if I have directly spoke with Tom (who spoke to the person he is leaving with), and the person I am staying with. Hand signals are only good for your immediate riding partner. Simply point the way you want to go, or wave if you need them to come in to talk. if you are changing your partner on the water, speak with them directly. We do not have huge surf, so it's not hard to get close for verbal.
I feel the same way about it as I do fighting fire. A crew is 3 (sometimes up to 5 in special circumstances), anything larger gets a second leuitenant so it actually becomes 2 crews working together. We go in as a crew, we work as a crew, we come out as a crew. Any member of the crew split to another crew is handled with direct verbal communication with confirmation between 2 officers. We do it this way, because when we don't, bad things happen.
Technology is only as good as the system as a whole. There are panic buttons that might notify the coast guard, but no technology I know can substitute good team work. People should take the tiny bit of extra effort it takes to stay with their riding partner and react immediately if they are not immediately present.