They just need to make raids a lot longer and more challenging, then put like a 3-5 day lock out on it. I'm talking about dungeons where clearing trash mobs is a challenge. Make each dungeon have an entire gear set (including jewlery) for every class, and have one piece drop from each boss (that means like 5+ bosses per dungeon) and 1-2 pieces ALWAYS drops when you kill a boss. Then make like 3 more of these dungeons with different gear sets with different stats, so people can mix and match stuff to customize their gears.

The longevity comes from needing to get all the pieces for the gear sets for all your classes, and having to wait for the dungeon to be available, not because you have .000001% chance of even getting something. If you have many different dungeons with long lock outs, you can do something different everyday, the content lasts long, and someone gets something everytime you go out.