Potentially nothing, but apartment buildings don't move, so an artillery shell at one-hundredth the cost would probably be the preferred option anyway for nations motivated toward such things.
Well, I've seen our allies use a $249,000-a-pop FGM-148 Javelin anti-tank missile against a solitary soldier where a $0.49 rifle shell would do [1], so I don't price matters. Especially when we're giving the stuff away.
Nothing, but they can do that already. Since residential apartments don’t often come with anti-air defenses, they’ll be guaranteed a hit with a high quality, precision missile.
These missile are about overwhelming quantities in a hostile environment. We’re basically seeing this in the Russia-Ukraine war, in two different ways:
* some missiles attacks will be a mix of high precision weapons and loads of low precision weapons. The low precision weapons eat up air defenses allowing the high precision weapons to hit their intended target.
* “cheap” drones are sent in large quantities. Many will be shot down, but enough will make it through to targets to be effective.
As anti-ship missiles, you can imagine how huge quantities could overwhelm relatively limited number of available defense assets.
You'll have to rip out the whole seeker to do that.
And even Russia isn't shooting missiles at apartments. Rather, they are shooting missiles at things they consider a military advantage to destroy (although Geneva would disagree with some of it--things like taking down the power so the people are cold isn't acceptable even if you gain advantage from it) and their guidance systems are junk.
And a lot of what Russia does looks very much like the result of a boss making impossible requests and not listening to reason. The underlings do whatever they think is as close to the request as possible, even when it's just flailing.
