I really hope so too. Unity really limits the amount of zombies you can have at once. It sucks so much to have a zombie game, but the world is empty af. I rather can´t destroy literally everything than having nearly no zombies.
It´s not going to be their next game though. They are working on a game with Unreal Engine 5 for some time now, but we only know it´s not going to be 7 days to die 2.