(If you want to argue that this is a realistic response, please explain how doing so would not be acts of war, inviting both retaliation and much worse acts then justified by ours.)
I don't expect the US to start handling this that way any time soon, but I'm not sure it'd be irrational for a nation to decide a cyberattack is, in fact, an act of war.
Even once that's all decided, we'd need to figure out if war would be a reasonable response. I'd propose that one of the main reasons the US hasn't ever escalated the situation with North Korea, even if we ignore China's likely response, is that actually subduing the populace and occupying the country would likely be extremely difficult. It's unlikely that a thoroughly bombed North Korea would be any more stable and friendly than the current North Korea.
War is extremely inefficient at bettering the lives in any of the countries involved - there are times when it is necessary, but it should be avoided whenever possible.
China is literally the only reason the US tolerates North Korea. And China solely tolerates North Korea because it causes all sorts of irritation for the US. Arguably, it would be better off for everyone living in North Korea if one of those two powers annexed it outright, but geopolitics loves backwater proxy wars.
Closer to the active phase of the Korean War, the USSR was also a factor. Today, the US distaste for instability, and naiton-building, and North Korea not having a hoard of oil or something similar to overcome that distaste is also a reason, today.
This is an unpopular opinion, but I feel like we should generally accept nation-building doesn't work well, countries we leave tend to go back to being horrible in a number of years after we set up a new nation there. And accepting that, and accepting sometimes that countries are completely failed, harmful to world security, and larger countries need to intervene: Annexation isn't actually a bad concept. It's absolutely frowned upon today, but I'm not sure is worse than what we've done to half a dozen countries in the past couple decades alone.
The barrier to war should be high, but at the point you obliterate a nation's governing structure, defenses, and likely civic infrastructure, you should accept you have a permanent responsibility for the civilians there. And maybe the best way to be democratic about it is to establish a process that states one annexes can petition and vote for secession after they've reached a more stable position.
> North Korea not having a hoard of oil or something
There's that. North Korea is a property that literally only Kim Jong Un wants. And major powers seem perfectly fine to let him have it as long as he mostlyish behaves.
If US government authorizes the NSA/CIA to infiltrate/attack all bitcoin exchanges that accept payments from wallet ID with ransomware, the problem likely be solved very quickly.