This is one of those ideas that is fun to speculate on, but highly implausible to implement. The premise is that by traveling with others more frequently, the more familiar you get with them and can work better as a team. It offers a little bit for everything - bonuses for static groups, additional motivation for pugs, a little more for power gamers to tweak their toons, and a little RP flare for people to modify their characters.
Each time you complete a quest with someone in your party, you gain +1 Familiarity progress with them.
Rank 0 - Stranger/Unfamiliar
"Stranger" is the default rank when you come across another character, and motivation to join pugs. If you party with 2 or more characters that have Stranger status, you receive the "New Adventures" bonus. Each stranger in your group provides a +2% drop rate for rare items on Heroic, and a +1% drop rate on Epic; this stacks to a total of +10% and +5%, respectively.
"Unfamiliar" is an alt countermeasure. If a character has rank 1 familiarity with yours, all of their alts are considered Unfamiliar at rank 0 instead of Stranger. An Unfamiliar character does not count toward the number of Strangers you need to initiate the "New Adventures" bonus; however, if you do party with enough Strangers to get it, they do add to the bonus to drop rate.
Your Familiarity progress with Strangers/Unfamiliars decays at a rate of 1 per day.
Rank 1 - Acquaintance
This rank is earned fairly quickly (8-10 progress), and reflects you are starting to get to know the other character a little better. They no longer trigger New Adventures bonuses for you. You can toggle the choice of locking the progress, or letting it decay. If locked, it will not go down over time; if toggled, it decreases at a rate of 2 per day. Once the progress reaches 0, an Acquaintance goes back to being Stranger or Unfamiliar.
Ranks 2-4 - Title Ranks
Each time you reach a new rank, you select one title to describe the other character. This provides a small bonus when you are close to the other character. You may choose the same title multiple times for the same person, increasing the title's effects and potentially unlocking new effects.
- Comrade - You trust your comrade to have your back in a fight. When you are within a short distance of your comrade, you receive +1 AC and +2 PRR. If taken twice, you also receive +1 to saves.
- Friend - You consider the other character a true friend. You receive +5 Positive & Repair Spell Power when healing your friend. You receive +5% Healing Amp when healed by your friend.
- Mentor - You view the other character as a mentor, and you learn much from their example. You receive +1 to all of your skills while within a short distance of the mentor.
- Teammate - You fight more fluidly and work more tactically with your teammate. While you are within a short distance of your teammate, you receive +1 Hit while flanking and +1 to Tactical DCs. If taken twice, you also receive 1% dodge while within the radius of your teammate.
- Rival - Seeing your rival excel in combat drives you to try and surpass them. Whenever your rival kills an enemy, for the next 10 seconds you gain +1 Hit, +2 Melee and Ranged damage, and 2 Spell Power. If Rival is taken twice, this effect goes off whenever your rival kills an enemy or scores a critical hit, and the ability can stack up to three times. If Rival is taken three times, it can stack up to 5 times. All stacks vanish at the end of the timer.