Anyone reading please feel free to tear this apart / add your own idea.
Create a reward/weapon/skin/tag/ephemera/etc that is very very cool, but is locked behind an "almost" impossible mission.
The reward may or may not be for the clan as well.
The reward may or may not be a special part of outfit for operator/frame armour etc.
I am thinking of something like MR tests, but much harder. So hard in fact that only the most skilled players will be able to get to it.
To counteract special abilities, like whisps ghosting or Lokis switch teleport make No Ability Areas or something of the kind.
Complement parkour with high level enemies like lvl150 that can one shot you if you dont dodge, get operator only section...
Basically just combine different aspects of the whole game to make players go at this suicide mission again and again. (Need to have amazing reward)
To counteract the high mobility of frames / operators, increase the distances to light years between platforms, etc.
Make certain focus schools be more effective than others. Like void dash may get you some section but will hinder you in others.
The goal is not to rely on RNG at all. but crank the difficulty so high that it's impossible to do.
And that will be endgame mission warframe style.
Create a bunch of these missions, combine them into a dungeon and you have a full set of endgame missions targeting solely the most skilled players, be they MR10 or MR27.