I think the compromise here would be able to allow members of different companies to assist with other caravan security missions. You have to be of the appropriate company to initiate, but your party members could join you in on it. Similar to the leves, where you may not get the full reward, but at least you can help in combat and not just be on the sidelines.

@ZDamned, unfortunately most players having been around as long as they have and being forum go'ers too, don't take into account a new player that starts up and plays the game more than browsing websites and forums. And as you said, nothing in-game quite indicates you will not be able to participate with your friends from other GCs on caravan security.