"I still recommend taking out the North Korean missiles, nuclear weapons and leadership but use conventional weapons. An FAE and a few bunker busters would work."

I'm sure that's been considered, but there are problems or it would have already been done. For one, Seoul would likely be turned into a sea of fire from the roughly 20 thousand artillery pieces targeting it. A whole lot of unhappy and dead Southerners the result. For another, China would likely go ape with unknown consequences. And then there's the likely possibility that you don't get all the nukes and/or the brain-trust that builds them( are you also prepared for an all out invasion of the North too track them down?). Too many things to go wrong in  a high risk action for relatively little gain. Better to work on striking a deal of some kind, like say a final peace treaty.