I know it sounds like a far fetched idea which will remove the element of zombies, but hear me out, we divide the entire map of zomboid in various smaller chunks, and add a percentage sign to them, and we can clean that entire area but once we do that, the other untouched chunks percentage should lower down a bit to fill up the chunk we just cleared out to a certain degree, as we don't need zombie farmers who just sit in one chunk and farm the whole map with that, and to increase the difficulty we will add a hidden progression bar, as the x number of days pass by the zombies should get stronger, and harder to kill, and now the issue is here that whose pc can generate 40000 zombies, and the answer is easy, we allot randomness in every chunk and random spawn in every chunk but limited to the percentage we mentioned and they cannot leave their prescribed chunk either, once the mc leaves the specified chunk they respawn again, as per the chunk, now if someone kills every zombie than what? well here the dlc's come in, which we can add, or maybe once the 0% is achieved, kudoos to them, and in online we can just increase the number of zombies once a player dies with some multiplier.