I personally think Blizzard doesn't do enough for 5 mans. I am pleased with what they are doing with WoD for 5 mans with leveling dungeons (only 4 but still), normal mode dungeons, heroic mode dungeons and challenge mode dungeons. However, some of the rewards may not feel satisfying to some, likewise to me. Since LFR will have gear that will be more powerful than heroic modes 5 mans.
So I kinda want to consider possibly having a mythic mode for 5 mans. However, instead of dropping gear, I kinda want to add the suggestion of adding only cosmetic armor. New armor. New art. I feel like mythic mode (it doesn't have to be called mythic mode either) will do it some kind of justice.
The difference between Challenge modes and Mythic mode will be that instead of times run, it won't be timed and the enemies/bosses will have more hp/dmg/possible abilities. So Challenge mode rewards unique weapon art, mythic mode rewards unique armor art likewise with MoP.
I only say this because even with challenge modes, there has always been the widespread notion with the endgame players that challenge modes just aren't satisfying enough. I personally despise timed runs. Never enjoyed skipping trash, always kinda ruined my immersion in some way.
Thoughts.