С4 was unbalanced, yes. But you know what? It was too weak, that's the imbalance. You only needed to get 200 metal for door and around 400 wood for rest to place a room. People would need a lot more to craft 2c4 to blow it. With that broken system there was no way to raid someone who play as much as you do, because he would always build more then you can blow. And if Garry would ever read player feedback, he would know it.
So we need system that would allow to raid big groups of people who play more then you. And there is a solution - key, that can unlock whole base. But no, wait! There is a perfect place to abuse:
1) First and most simple - big groups will always leave someone as a housekeeper, he will lock doors behind everyone and house will be safe. They just gonna change the guy, so everyone would need to stay on guard once in a while. That is 100% raid protection. They could even use account of their offline friends to do it, so - if you play with friends, you could not fear about being raided.
2) If you spawn inside and lost key outside you are locked. People will not even need to raid each other - just take the key, drop it somewhere, and - any house destroyed.
IF you can craft more keys - what prevents enemies from coming to your door and do same? If you will be able to craft more keys there will be door ownership, and then we coming back to where we started.
3) Without c4 anyone can build walls around your house and just lock you inside. You cannot blow walls, your house are screwed.
4) Another way of being 100% protected - going offline. There will be no more way for a single player or two friends to punish big group of players - before you could wait for them to go offline, and then outsmart them, find out where is the resource room and raid it. So people who will play in big groups will have even more advantage, becuase they can rely on their numbers only, and do not need to make smart base to protect their stuff from being raided while they are offline.
There is no more point in sleeping bodies anymore - all you need is to not sleep outside of house, and you are 100% protected.
5) No use in metal structures anymore. Well, i think that is why dev's not doing even arts about it. So people will use metal only to craft guns, guns guns and more guns.
And game will become some kind of casual open world shooter, people will just run around and kill each other, end of gameplay.
UPD: Already found a way to abuse system even more easy then before.
What we need? Main house and the temporary storage (just one room with boxes).
What we do? We craft a key and sleeping bag. Putting bag inside main house, then going to the storage house. Putting bag there, then coming back to main house. Putting key from main house and from storage in chest, suiciding, spawning in storage, putting door in storage.
So from now, when you gather enough resources and stuff in temporary storage, you just need to make sure nobody is around (maybe ask friend to cover you or just help you, that wold be more easy, but you also can do it solo), suicide 2 times in a row. You will spawn in main house, open in with main key, then open storage, take stuff, move it to main house (you can place it right near), lock the door again, suicide.
All hail to the suicide base return and for dev's, who can think before do something! >_<
That is the most easy way to keep everything you have safe - even if you die outside, people who will loot your key would be able only to open temporary storage when you will keep few guns and a bit of resources, but you always can build a new one. The main house will always remain locked and secured.
And that, my friends, is how you use brains. Way around found in a 10 minutes after seeing new key system.
I am pretty sure that eventually they will just replace num locks with keys that cannot be looted and forget about current crappy idea.