What if players can create their own objectives ingame and be rewarded for it? Goals like, ogre hater, orc hater, night elf hater, pirate hater, wolf hunter, bear hunter, Rare hunter (all of those involve killing as much of those as you can), Killing people who kill animals, collecting certain items, band aiding injured players, buffing other people, etc.
Then players get rewarded by something like adventure points that you can exchange for gold, gear, proffession mats, or cosmetics. Cosmetics like, hats, beanies, bandanas, wolf head helmets, tabards, etc.
The reward is balanced based on how hard the task is. Like killing elites gives more points than killing critters. Also there is a limit on how much you can farm per zone so you get to explore the world and help it feel to be less repetitive. There will be a limit on how much adventure points you can earn daily just so you don't get too ahead. Or you can earn as much points but it diminishes how much points you can as you reach certain points. You can also find people on the same objective so its a single player content that could become social too. Maybe you can only have like 4 active roles at a time, so you can focus on a few things at a time and meet other people doing the same. You could also find other people with the same role in lfg. It could also go hand in hand with other content as it will send people out to the world and do something.
(i've updated this post)