I like what Mass Effect 3 did... Community challenges. Throughout the weekend set a goal i.e. Vanquish 35,000,000 Thrall in Patrol on the Moon. As a community complete 5000 Vault of Glass and 5000 Crota's End raids. Etc... When these community goals are met, a package containing Challenge Specific loot is awarded. This loot should be random. Giving the community a common goal was fun, add a progress bar, and bam you've got another level of challenge for the gamers to work toward.