[CaptSkip]

How long would it take to get that level of US assets into the Korean Peninsula?

A heck of a lot longer than it would take the North to move a million+ soldiers thirty miles from the DMZ into Seoul after destroying most of Seoul with artillery.

An "Emergency" to save South Korea would likely require the US to use Nukes on the North if there is to be a chance of saving Seoul and the South.

[Strategerist]

I doubt the North Koreans get very far at all, even with no US reinforcements having arrived.

DMZ troop densities are very high and it's been fortified for 50 years.

Regarding Seoul and artillery, only a fraction of NK's tubes have the range to hit Seoul from the DMZ. A lot of articles make it look like every artillery piece they have would be firing on Seoul.

Anyway, the NKs would have invaded the SECOND they thought they'd be successful. They haven't. And the correlation of forces isn't getting any better for them. So they won't, I suspect.