Well, since the experimental Z-levels are working somehow already, I felt some things are definitely not quite worked out yet.
Seeing that cataclysm offers the chance to not only clear out towns and make safe heavens with static spawn (and even with dynamic spawn if the world settings are done right) the lack of content for base building is quite feelable.
While this might not be high priority at the moment seeing the NPC and vehicle overhauls, it is definitely one adding quite a bit of long-term fun in an easy way.
So, my thoughts about it:
At the moment it seems like the floor and roof are handled as a single tile in the game, with stuff in the middle. Changing this up to having each z-layer consist of several ‘hidden’ layers would be a good way to make it happen. Said layers would consist of the floor, the space in the middle and the roof. The changes would keep the feeling of the game intact while adding a lot of customization option.
Having the roof act as a walkable space at the z-layer above opens of the possibility for a far more advanced base building concept as the player can change the layout of a building in each way imaginable.
Which brings me to the first thing that was suggested quite often: Non vehicle power grids.
This is a tricky one as only vehicles are powered at the moment, while static tiles simply don’t have the option to be like this, implementing several new constructions could change the problem of vehicles being the only useful way of setting up a base. A power supply, a way to conduct said power and energy using constructions would be needed for that.
How could it work: Using for instance a swappable battery case could be the energy storage of said systems, the flooring can be made conductive (wired wooden floor, wired rock floor and so on) as well as walls being made like this. Energy creating tiles like reactors, solar panels (definitely very weak makeshift ones as well! 1/10 energy production as a suggestion), wind energy or anything else in this direction.
The system then simply checking for power changes whenever a tile is destroyed or newly build, making background ‘vehicles’ out of it able to consist of several layers. As an example:
We have a generator type tile, wire type tiles and consumer tiles. Imagining a wired wall on the lower z layer and a wired floor above it with a lamp on the tile. If the wall underneath is destroyed, being a wired tile, the game could simply remove this one from the vehicle layout in the background. If there is no connection anymore, then a single vehicle will be made into two, and vica-verse.
While still being a similar system to the one already in place, it would need to support several z-layers, as well as the dynamic breakup into several vehicles, or fusion into a single one.
Another part is the missing customization part for homes. While we have carpets and paint, there is no way to produce your own, especially carpets should be made a tailoring recipe, either needing rags or probably rather felt, as well as a way to get the color. Adding colors could be done by using several items either already present (Black = charcoal for instance) or things which are used for dyeing items IRL.
It adds a good way of customizing a future NPC outpost which is managed by the player, making a proper hideout which isn’t only functional, but nice to look at too.
These things could lead to proper elevators (rope & pulley system using for instance, or powered ones) automated turrets for defense, electric fencing and even industrial sized production options for future buildup. With NPCs getting more advanced slowly it just makes sense for the survivors to try and find ways to produce important items for the cataclysm themselves, even if theirs are inferior ones like the refilled ammo. It would open up the option of making your own serums for instance, or low-grade solar panels, maybe by taking over key points in the game. A chip company, electronics producer and things like that. It would open up another path towards the end-game then simply shooting your way trough hordes of zombies and steadily getting stronger, instead building up a society of survivors adapting to their new life and building up civilication in a new way (and probably not quite human way)
As for making this even doable. At the moment the game severely lacks a proper transportation system besides megavehicles (which are fun, but absolutely weird as well), at least fluid-wise. It’s a chore to get big containers besides 60L Tanks as they are rare as could be. My suggestion would be to add a rare location with specialized items to the game, one that makes sense gameplay wise, as well as adds to the reality part. The main fluid transportation other then tankers are the commonplace 1000L plastic tanks, seeing as the game only uses big kegs for now this would not only be an upgrade for the future (getting a central point for npcs to get their water for instance) but also a needed implementation. Keeping yourself alive is a chore in the first year, as should be, and still is a chore later in the game. Finding big containers over 60 Liters is quite hard, and either you have to build 200L drums, or be glad to find some barrels or drums somewhere else. Those 1000L ones would help out greatly to keep a big stack of water at hand, and together with proper implemented farming could lead to a self-sustaining survivor camp without the the hassle of managing several darn small containers. Other then that, why not a proper water tower? 1000L is a small amount, especially when people need to use it for all sorts of stuff like cooking, drinking, maybe even showering (morale bonus would be fun for that) and so on.
It puzzled me since the first day why there wasn’t a single big container in the game after all, having grown up in a family of farmers and winemakers, I’m used to seeing quite massive sized ones after all, ones that are still transportable if empty as well but are still missing in the game. There are massive amounts of houses and shops in the game, but nothing were they are getting their materials from by now.
As I don’t know which things are already planned, or which are actually easily implemented I simply threw them out like this, and seeing some of them implemented in the future would be great.