The first time I killed a Faceless, my natural thought was "can I now remove its mask?"
I think there should be a Biology skill check to examine Faceless corpses.
Moreover, maybe it could unlock a special feat if you examine enough corpses. Say, you can now craft infusions with Deep Caverns components. But, as a tradeoff, all Faceless are automatically hostile to you.
Here's why I think is a good idea.
1. It's balanced imo. The Deep Caverns become much deadlier, but you are also stronger. Moreover, you're only stronger for the Deep Caverns and afterwards, since before then you won't have the components to make infusions. So crucially it doesn't affect pre Deep Caverns difficulty.
2. It incentivizes playing differently. I think most players try to remain at least neutral with the Faceless for obvious reasons. This could change that.
3. It makes sense that a character with high Biology would do this. And it's a natural way to add some interesting lore.
Even if you disagree with there being a feat reward, I think there should absolutely be the option to examine Faceless corpses.