I'll start with the minor suggestion, and while it is minor, it is very important that I ask; Could there be a multi-parent relay implemented? that or just applied to all relay? I've found it very hard to set up a two way door with switches when only one switch can connect to the door to activate it. If multiple switches are lined up it would make sense that they function in unison, ie: if 3 switches are lined up to each other then a door, all three switches would need to be active to open the door. This would allow for more easily set up electrical grids where multiple switches could activate one source from different locations, or persons could make a complex placement of switches to create a central control building or grid for various contraption.
An additional minor suggestion being 2x2 doors since you can't face two doors towards each other.
The major suggestion, practically overhauling or adding new AI, by adding human Npcs that aren't traders.
Perhaps the player could find other survivors in abandon buildings waiting to be eaten by a roaming zombie or found by the player to be traded with, killed, or recruited to defend a base. This can be particularly helpful for solo players who may not have any multiplayer assistance, or for those who have a knack for civ type games. Perhaps these survivor Npcs could have skill points or combat points of their own, allowing them to specialize with certain weapons. They could level up and the player could choose points for them, or it could be automatic/randomized to the Npc. All of this could still be added along side a disable/enable survivor Npc option.
The implications of friendly survivors also imply hostile survivors and even raiders. Of course all of these would be rare finds, like finding radioactive zombies in the early game, but it could be a desirable addition for a zombie survival game.
I'm not entirely certain if suggestions are being accepted, much less reviewed, but if they are, I would like to offer my suggestions whenever possible. I would gladly contribute my extraordinary creativity, whether it be implemented or not, just having my thoughts read by another for possible consideration is thrilling. I'm not asking for money, not a job, nothing but hope that suggestions don't go unnoticed.