@Devs
I had an idea today you might find useful in regards to underground bases and address it in the future.
I understand the idea of the underground base is really appealing to players because of the safety it can provide, and that the core issue is how can you allow people to utilize this option but with a fair trade off. Not only that, but how can you make the trade off fit the core values of the game and the genre it wants to emulate?
My suggestion will allow for this option still, but make it much more difficult to do in the early game, and limit the amount of time players can spend underground in a fun and fluffy sort of way.
Make being underground limit the amount of oxygen available, and after reaching a certain depth there would be no oxygen. You can use mechanics similar to what water blocks use, but make them a hidden block that only occupies open spaces below the starting surface area. If you dig a large open pit you should be fine, with air being able to flow into it, however even then at a certain depth the air wouldn't penetrate.
So how do you dig underground bases? Air pumps.
You will need power, and air pumps pushing air underground for you to survive while you are down there. Animals will need to be included in this, and should be fairly easy to do an air quality check if they are underground to see if they are in danger, zombies however would be immune (as expected). Plants should be able to produce a small amount of oxygen, and underground growing an option using lights (but at a slower speed, maybe even cap their development to a tier or two lower than outside growth).
Add a pollution mechanic from generators that use gas, this way you won't want to be running them in an area the air isn't being pumped.
If you combine this with a water collection / hydration overhaul, and lingering hordes that hang out near the entrances of underground bases (both of these I already discussed earlier in this thread), I honestly think you can make it a viable and immersive option that will provide for some fun game play mechanics that fit the concept of this game better than having zombies that can dig.
I would love for some feedback and input from everyone, devs feel free to ignore me if you so choose (it is your game after all) and I will gladly not feel offended =)
