Hi, newer player to the game and I very much love the whole concept as well as how modular the game's sandbox is to create the experience you'd want.
One thing that I think could potentially be an area of expansion for the game is an option where you can limit the number of times each zombie can respawn - whether you think that should be 0 (no respawns), or a number 1-50 is up to you.
I feel as though many people will argue that the option of turning off respawns and setting zombie numbers higher is a substitute for limited respawns, but I would argue that for new players the idea of playing on higher zombie settings is a *very* big ask. The added immediate difficulty spike of doubling, tripling, or quadrupling the number of zeds you run into is insane, and in the end it still results in the in-game population still amounting to only 1/3rd the real-life population at the time of the event.
On the other hand, I've tried playing on normal zombie pop with respawns off, and... it's actually kinda easy. You can clear the whole area around your base before heli event, even if you're not very good at the game. If you're bold enough to clear the scattered zombies around your area day 1, you can continue to clear those that flow in over the following days and prevent your area from ever hitting peak population. My current balance is no respawns with a 1.25x zoombini multiplier, but it's not perfect. If you want the game to remain difficult, you need to continually up the modifier as your skill increases... and even then, once you "break through" the population in a No Respawn save, the difficulty curve of the game falls off a cliff edge.
So, my proposed solution is this: split the map into a grid of some sort, dividing areas up into chunks. Rather than the very inefficient method of attempting to track 30,000 individual zombies' life count, my proposal is that you count the number of zombies that will spawn in the chunk at 1x population and count track the life count of the *chunk* as life count = [zombies]*[respawns per zombie]*[zombie multiplier]. I assume migration of zombies off-screen is calculated in the background, so if zombies are going to move from one chunk to another I don't believe it would be that difficult to just take some of that chunk's life count and migrate it along with them. Each time a zombie dies in the chunk, reduce the life count by 1. As it runs out, you could slowly lower the zombie count until eventually the zombies just stop respawning entirely.
The result?
A zombie respawning system that could be set to 10x and near-accurately recreate the real world population of the area, without adding or subtracting from the early-game difficulty curve. Areas cannot be cleared via one big sweep, but concentrated efforts can whittle the zombie population to zero.
I consider this system a direct upgrade for those who don't want the hordes to be literally unlimited.
Thanks for reading