Trading could work, but it would have to be very complicated. Let's say that you and your friend are both level 20 (max level) and want to trade. You are able to use any piece if equipment (character specific) at that point in the game. Bungee has said that at that level you just begin to obtain better gear to do harder strike missions. But, say that you've spent only 100 hours and your typical armor piece find has about 100 defense whereas your friend has spent 300 hours and typical armor piece find for him has about 300 defense. Now he can give that directly to you and save you that 200 hours of grinding away on strike missions. This is a problem and they would definitely have to look into a solution or else this would totally ruin the game.