Throwing out my ideas which highlight, use, reinforce many in this thread...

Player slain - click to harvest. Brings up harvesting of:

-Bone - obviously bonecraft
-Meat - Food
-Skin - Leatherworking
-Head or ear - Bounty system, religious rewards, etc

Religion & Alignment - Make various consequences/bonuses for doing these. Obviously a good aligned tribe would lose favor going around skinning people and making silly masks with their opponents faces. An evil tribe could be even more outcasted from other tibes (even evil ones) for doing this. Good tribes could take the ear/head for bounties/religious purposes for no penalty but only bonuses or barter/currency/favor. A good tribe can have it seen via religion as killing/stopping "heathen" people, thus gaining favor or relative compensation, and the opposite for an evil tribe possibly giving them favor for appeasing their gods/belief.

Politics - This would also add political depth to the diplomatic sphere of the game. Tribes with similar ideals, good or bad, would work together to stop or thrive from cannibalism. Obviously, if an evil tribe is known for camping/grieving a good tribe, we could see things like:

Evil tribe using heads on pikes as deterrents, as antagonists, as fear of trespassing, various other aspects. Evil tribe is able to make clothing/armor/structures out of good/neutral aligned players. Obviously, if someone was wearing a business suit and armor made from my tribal leader while prancing around in front of my tribal gates...well...thats going to flat out piss me off and make my whole purpose in game to pay them back! Good/neutral players can get major benefits by destroying these structures/items/and people.
This would add major depth to the game and various options for ALL TRIBES, not just evil.

It would also open plenty of opportunities for guilds to "hire" each other. Example: Good guild member hires Neutral escorts for a trade endeavor to another tribe...but must travel through known cannibal territory. Thus boosting and adding depth to the player driven economy!

Crafting - TAG each item harvested in this manner: when you see "this item was created by X player" state "this item is from human remains" or "this item crafted from human remains". Apply desired penalties when said items are looted/equipped. Obviously limiting the trade because, if deemed as loathsome by tribe, could garner major penalties. Else, reap benefits of cause/effect/tribal influence/ etc.

Adds major dept to many things being crafted from parts of humans. Structures could be adorned with, or created from, human parts. Examples - heads on pikes, thrones for tribal leaders made from enemy bones/skulls, tents from skinned human flesh, etc.

Weapons crafted out of human bones could supplement religion.

Armor crafted out of human bones could do the same. Clothing/Leatherworking the same but with different designs. This could supplement a guilds "look".

Good/neutral alignments could gain bonus favor for destroying all the aforementioned. Evil cannibalistic tribes could just find more loot!

Respawn and Death - Players that would have this happen to them would be forced to respawn per respawn rules. I could see this logically working as them respawning at their tribe's totem or in their village. I detest global graveyards since they are generally a place of camping/grieving.

Lore and Roleplay - For those that enjoy this aspect of the game would obviously have a field day with this. Criticizing those that did it, fighting the "vile eaters of flesh". This IS a post apocalyptic world, it would be likely that someone is going to eat someone else...especially if food is scarce.

*Many RL tribes believed that consuming their enemies would give them their power or spirit. The majority of religions deemed cannibalism as taboo and greatly punished/scorned those who did it. Im just rolling with these ideals.

Ive never truly seen this idea as potentially working in a game before but greatly believe this is a phenomenal idea for this one. The main sticking point, imo, is BALANCING it to have equal benefits for all good/neutral/evil. If balanced, this idea could add major content, fun, and much more sand to an already incredible sandbox!