Seven deadly s(k)ins?
How about a bunch of skins with a theme of the 7 deadly sins:
Pride: 
Greed:
Lust: 
Envy: Ummmm.....
(cos he wants friends?) or 
Gluttony:
Wrath:
Sloth: 
(cos the clone does all his work?)
70 Comments
#7 DEADLY SINS:
PRIDE
GREED
LUST
ENVY
GLUTTONY
WRATH
SLOTH
#4 CHAOS GODS:
LORD OF SKULLS
SHE WHO THIRSTS
THE CHANGER OF WAYS
LORD OF DECAY
#4 HORSEMEN:
WAR
PESTILENCE
FAMINE
DEATH
#EDIT: WHAT SOME PEOPLE DON'T UNDERSTAND IS THAT THIS LIST IS WHAT CHAMPIONS I BELIEVE WOULD HAVE A COOL SKIN BASED ON THE THEMATIC I LISTED, NOT THAT THEY ARE THE PERFECT OR BETTER REPRESENTATION OF THE THEMATIC. EXAMPLE: YOU CAN SAY THAT VARUS IS PESTILENCE BECAUSE OF THE THEORY THAT THE DARKINS ARE BASED ON THE FOUR HORSEMEN, BUT WHAT PESTILENCE LIKE SKILLS VARUS HAVE TO LOOK COOL AS A SKIN?? HIS PASSIVE COULD BE GREEN BLOBS INSTEAD OF PURPLE? NOW LOOK AT SINGED, THEY COULD ADD A GROUND EFFECT OF THE LAND BEHIND HIM DECAY AS HE WALKS.
Tahm is greed, not gluttony. Gluttony is only linked to his current appearance (the one he assumed for Tahm Kench the human). Greed defines him as a whole.
Wouldn't Kog'Maw be gluttony?
SEVEN-IN-ONE xD
I would rather these Skin were made for champions who don't usually embody that Sin, e.g.: Lust Sin Soraka, Pride Sin Amumu, Sloth Sin Ekko, etc.
Sloth: 
(just lets the yeti do everything)
The majority of Void champions can be gluttony, I feel. The majority of them want to devour, after all-- although Cho'Gath is the prime example of this.
I'd say Cho would be Gluttony, and Gragas would be Sloth.
Why is cho greed?
I love that you ignore that Nocturne is a demon of Wrath.
We have:
Evelynn demon of Lust
Nocturne demon of Wrath
Demon of Gluttony
Itd be weird for them to have skins based on themselves.
I understand Eve should be lust because of the way it looks now, but I don't feel like it embodies Lust. What it is now is just means to an end. It could be whatever it wants.
My Humble Opinion:
Pride: 
Greed:
Gluttony:
Wrath: 
Envy: 
Sloth:
Pride:
Greed:
Envy: or
Wrath:
Lust:
Sloth:
Gluttony:
I believe the Demons themselves already represent them as Tahm is a sin - gluttony, personified and subsequently, Evelynn for Lust.
Last time I checked Tahm Kench takes advantage of other peoples' gluttony, he isn't gluttonous himself.
Xewrath Evelust Envarus
Edgiest skin line
Pride
Lust
Greed 
Envy
Gluttony
Sloth 
Wrath
for sloth
basically omnipotent, yet I don't see her in the lore.
Pride: Yeah, Draven or Jhin fit here, though I would say that Draven probably fits a bit better (the sin of pride is usually displayed as vanity in most cases, and Draven fits that far better than Jhin).
Greed: I think Gangplank or Sivir would fit better here than Cho. Cho is very solidly gluttony, not greed, while GP is a ruthless pirate and Sivir is a mercenary motivated only by money. Kench could fit as well, as he's pretty much called out as a manifestation of greed.
Lost: Evelynn all the way, she's a succubus (in the modern sense, not the classical sense).
Envy: Amumu might fit, but I think Galio could just as well, as he seems to be pretty envious of the living, and Viktor might too (for the same reason the Borg could be considered a manifestation of envy).
Gluttony: Tahm Kench would make sense, as would Cho or possibly even Kog'Maw or Vel'Koz (he has a case of gluttony focused on Knowledge.
Wrath: Renekton is close, but I'd say he's more anger than wrath. Kalista fits perfectly though.
Sloth: Zoe. She makes portals just to avoid having to walk, and doesn't take anything seriously.