Keeping the player base active after raiding "Idea".
I first of all want to point out this is obviously not an original idea I came up with or anything. Anyway..
Why not pull from another game the idea of progressively harder dungeons with greater rewards? For example, WoW's Mythic+ dungeon system.
Players start the week with a level 1 key for a certain dungeon. As you complete it in certain time periods you obtain another key which could be level 3 now. Then level 4, or 7 or 20. Whatever you end up getting to that week and it becomes so hard you can't go any further. Mobs/boss damage increases each tier of key, mob/boss HP increases the higher your key gets, and so on. The higher you go the greater the rewards you could potentially receive, with a bonus chest at the end of the week depending on what you got your key to.
The rewards don't necessarily have to be gear either, maybe chances of receiving a penta meldable crafting piece, a rare crafting material , a rare minion, whatever the case is.
Thoughts?