I have a strong feeling such concept was already reviewed.
Still it would be really interesting to see a real blind champion. Especially concerning recent improvements in visuals and gameplay.
[ General concept ]
Lee Sin doesn't have "vision" in gameplay sense. He is blind. There is no fog of war for him.
He can see everything in vicinity - champions, monsters, projectiles.
He can always see all terrain. Much like real blind people remember everything around their house.
[ Visual ]
Player sees mostly the same rift. Only "downgraded".
Visually everything looks different as if graphics shaders applied. There are no colors (not saturated at least).
There are no detailed textures (mostly outlines) on everything around him.
Lee Sin appears normally. As he is currently in the game.
[ Gameplay specifics ]
He can see over terrain and in brush with distance restriction.
His "vision" is stronger when object is closer to him.
There is no delay like for Rek'Sai tremor sense.
"Global". He can see (remember) all structures - turrets, inhibitors and their state change. And ally champions.
"Near". Wide zone like distance between two jungle camps (with interesting gameplay possibilities for invading). Monsters and minions (no enemy champions). Only silhouette without health bars or effects.
"Close". Right near him, on the same screen. In addition to above he can see enemy champions, projectiles, effects (e.g. shield, poison or Spellblade on champion). Health bar on epic monsters when right outside the pit.
I'm not sure about bushes and enemy champions.
It may be pretty OP to remove any vision restrictions. On the other hand enemy champions should be visible somehow.
Maybe it's impossible to see enemies in bushes (e.g. sound of bush masks enemies).
Or you can see enemies only when they move and in addition E or W can generate a sound wave that reveals surrounding enemy champions.