If Trump handles this the way he handles everything else, it'll be a great success for NK.
Regardless of political affiliation, we should hope that this somehow ends up in NK giving up its nukes and works towards reunification.
But the notion that Trump is the one who will do this is, as of right now, is utterly farfetched. On the other hand...
What does Trump know that every past administration and multiple nations didn't? I really hate to claim insider information because, well, Interwebs. However, I have a good friend who's still in the Army and he's relatively high up. He's been back and forth to Japan and SK about half a dozen times over the past year. While troop buildup hasn't been happening, what has been happening is a buildup of material to facilitate troop buildup. That is, the U.S. military is positioning itself to be able to much more rapidly and effectively deploy troops both from Japan to NK, and from the west coast to NK. In addition, Trump has ceded military operations to the military without question. Apparently, he's told the military to do whatever it wants. That is, there's little to no civilian oversight over the military. Finally, the JDF (Japanese Defense Force) is preparing to go with a kinetic policy rather than a purely defensive one.
The potential conclusion I'm drawing here is that the U.S. has been quietly preparing to actually go to war with NK, along with the support of SK, and possibly even Japan rather than maintaining the status quo, and NK knows this. Thus, NK may finally have been intimidated into coming to the table and giving up its nukes.
I only put this forth as a viable possibility, not as the reason this is happening. It's possible that all the soft-shoe negotiating has only ever confirmed to NK leadership that their belligerence works in their favor. But now, faced with Trump, a man who's never met the concept of forethought or subtlety, and who has given over any say in military operations, their existence may actually be in jeopardy.
But in the end, this whole Trump meeting with Un will almost certainly come to nothing and the embarrassment will continue.