Xsyon doesn't advertise itself as a horror/zombie mmorpg, so I'll probably get flamed for this..

but I would love to see a lot more elements of the survival/horror atmosphere and mutated zombies as the toughest npcs. I know this game is really big on PVP, tribal warfare, and native american-like culture right now, but I could also see a parallel move in future development of zombies coming in from the outside and survivors having to band together to survive against them.

There aren't many zombie mmorpg out there, and I think this would draw a lot of new players in.