Yeah, i don't know why there are still no mods with world like a shooting mark (at least i haven't seen any):But Necropolis is just like vanilla a sandbox, survival is the gameplay, if you manage to survive for a long time without dying then you are the king of Necropolis.
I will think about some kind of end quest, maybe players will be able to find a Beacon to radio for help ;D

When player spawns on outter circle and the main goal is to reach the center and get something. With each circle zombies are stronger and faster. And overall enviroment becomes more harsh with each circle.
Of course, such world is more like rpg and not sandbox, and we need a character that can evolve - with stats and skills. But still even here in 7d2d it would be fun.
Mods and vanilla - always about simply surviving. But at the point where you know you will easily survive, it's not a survival anymore. And then it can be good only for builder-guys.
Those who are not fans of just building stuff and "having fun" (like digging tunnel through all map or making underground castle etc), the game gets boring at some stage. And we seek for challenges.
Having a hard-to-achieve goal is rly nice.
In necropolis it can be even like: what happens first, you complete main quest or it will become so hard that you will not be able to do it anymore. When time is against you. But well it could be too much of a hardcore maybe

How much time you will need to complete main quest - also a good challenge.
Also about the water, it's not only easy to survive in. It's also that water can get rly close to a center sometimes.
Well, not only water can do this, but when water does this, it breaks the balance.
BTW, it's a shame that there are no voxel-based RPGs with magic (normal voxels, without huge cubes like in minecraft). And i don't rly understand why...