Main reason I say why not just do it is because if something ends up fun but drops nothing worthwhile, no one will do it unless they have to. A lot of MMOs suffer from this and even more so if you have the ability to see what everything drops ahead of time.

Example in FFXI; No one will do Einherjar Tier I if they had the option to because it drops nothing but synthesis materials generally -- Same with Tier II, which the off chance of a lower tier abjuration dropping. Everyone would spam Tier III or Odin if they had the option because that's where all of the good drops come from.

So if SE released a dungeon that's like:

Tier I = Most fun you can ever have. (Drops nothing but decorative items)
Tier II = Even more Fun (Drops nothing but decorative items)
Tier III = Horrible, you'll die every second you're in here, but it drops epic gear. (Insert Gear list)
Tier IV = Don't even bother trying without 98 people and 200 backup for the 1% CHANCE at getting even more epic gear (insert Gear list)
Tier V = Hell, but has the best gear at 100% chance of dropping (Insert Gear list)

Guess which tier people will flood to? This is why a bit of mystery is good.

To each their own, but generally playing is all about finding out new things; How I see it anyway.