Now that we've got syndicates and more of a social atmosphere inside the game, I'd like to suggest player-to-player trading as a next big thing feature.
For example, trading could consist of two consenting players exchanging some combination of cash and items.
That would make sense for a few difference scenarios:
1) Two players want to buy/sell items for cash.
2) Two players want to barter for more desirable items.
3) Player wants to help gear up their syndicate noobs.
4) Player wants to gift a bunch of gear or cash to a friend.