I always thought that combat was the best part of the story. Then again I don't really like that whole gameplay/story segregation thing.
I hope PE uses vancian casting. After DA2(I was ok with DAO, since cooldowns for the more powerful abilities were a bit longer and global) I really don't want to play another cRPG with a cooldown system.
My favorite memory was playing a PnP game of Rifts. The group were superhumans who were doing battle with vampires in Mexico. We ended up destroying roughly half of the world. Glorious.
"Custom" spells would be quite good. I don't see any reason, other than cost, why not to include such a feature.
Also I think that something like metamagic(from D&D 3/3.5) would also be an interesting mechanic.
It should vary from culture to culture. I could see a female dominated society that regards males as little more than cheap labor and walking "sperm banks". While there could also be a society that sees genders as relatively equal.
Limited ammunition please. However, arrows(and stones if there are slings) should be relatively easy to craft with from variety of materials that can be found in the wild.
Lets see...
Serial Killer
Kingpin
Bigot
Pirate
Kill family members
Hermit
Vigilante
Slaver
Commoner
Pretty much any other "unpleasant" thing that other RPGs restrict so they don't offend anyone.