It would be cool if they implemented a "Friendship Meter" that allows people on your friends list to become better acquainted with each other by gaining exp together through dungeons and fates and such (fates will be nerfed in ptach so dungeons will be better exp gain) It can be like this:

Level 1: +2% hp bonus if friend is in party*
Level 2: +2% mp bonus if friend is in party*
Level 3: +10% def if friend dies in battle**
Level 4: +10% atk if friend dies in batte**
Level 5: ilvl 1-20 now trade-able between friends***
Level 6: ilvl 21-30 now trade-able between friends***
Level 7: ilvl 31-40 now trade-able between friends***
Level 8: ilvl 41-50 now trade-able between friends***
Level 9: ilvl 51-70 now trade-able between friends***
Level 10: ilvl 70+ now trade-able between friends***

*= non stack-able
**= non stack-able, duration 30 sec
***= items can only be traded, will still follow unsellable restriction