It'd be great if the designers could implement some game mechanics and rewards that foster positivity.

The current DF system doesn't really foster positivity because of the anonymous nature of playing with other people who may not even be in your server.

I think they should add a "comrades in arms" social list where you can add people you had a good experience with in a group. It would be awesome if you could use this social list to form future groups with these other good players. They could even add a small stat/exp boost called "battle buddies" or something that stack the more you play with the same people. It's like an in-game reflection of your deepening relationship with the people you go to battle with.

These are just some off the cuff ideas for game mechanics that could foster a better community and empower more types of players to find good groups.