I don’t know if it is possible to add functionalities to the forum, but if it is, I have two wishes/idea’s:
Followers
You can follow others via their profile.
You can opt in to receive notification whenever someone you follow starts a new topic or posts a public message. Would be amazing if these notifications were fully customizable (as in for each person different settings).
The amount of followers is displayed on the profile and therefore people with more followers will likely have a good community reputation.
Friends
Another idea for community binding is friends.
You can send a friend request to anyone. If he/she accepts, you become friends, and you will both be featured in each other’s friends list on the profile.
When creating a private message, a friends list will appear so that you can easily select a friend to write a private message to.
Similar to followers, you can opt in to receive notifications when your friends create new posts.
You can turn off the ability for others to send a friend request, or you can limit it that only people you follow can send you a friend request. This is for anti-spam, especially for popular accounts.
Both features also enables more potential badge ideas, for example: