This is a good sign for a long lasting peace in Korean Peninsula. I hope it will continue to the goal they want. And maybe the unification of two Korea's just like in Germany.
However, now it is hard to make a prospection what influence this doc really have. Will hope that situation will be changed for the better.
The document itself is little different than previous agreements that NK has participated to in the past. The difference this time is that in the past, the US was willing to essentially give money and sanctions relief what was basically up front, which is not the case now. In this agreement, the US agreed to stop military exercises with South Korea (which were little more than a show of force to NK), and security guarantees that last as long as good faith negotiation continues. There was also the threat of military action on the part of the US, and Trump seems to be willing to use military action against NK if necessary, which I don't think was the case with previous administrations, certainly not the Obama administration.
It will be more difficult in my opinion. The mental and economic difference between Koreas is bigger than it was between Germans.
Germany being reunified was the result of the USSR collapsing (in essence). I don't think the NK government will fall, at least not without the help of a foreign (to NK) government as NK has too much control over their people. Although like the USSR, NK appears to be rapidly running out of money.
I think its quite simple - if kim wants to stay in power he will not give up nukes.
I don't think it is that simple. The Trump administration, in conjunction with the UN, have placed strong sanctions against NK, making it difficult for NK to fund its operations. There are various rumors as to how much money NK has left, but the general consensus is that it is not very much, and they are having more and more difficulty selling what little exports they have.
Kim is in a difficult situation. If he gives up his nuclear weapons, then he's quite likely to be Libya'd.
Kim was given some security guarantees by the US, and the US needs to keep this agreement if it wants to have any chance of reaching a deal with Iran. If the US reneges on security guarantees, the chances of war breaking out with Iran go way up, and if Iran does successfully develop a nuke, they could potentially sell it to a terrorist organization (or potentially even the underlying technology to a terrorist organization), which would be good for no one.
Probably, Kim is not really interested in change, and he'll basically just ignore this.
In the past NK was able to renege on stopping their nuke program because they were given nearly everything up front, and has little to gain by keeping their end of the deal. There is also the issue of money and sanctions as the Trump sanctions against NK have reportedly been particularly effective and there have been reports that NK is low on money.
I suspect that it was mostly set up by Tillerson before he was replaced...)
Pompeo visited NK when he was still the head of the CIA, and Tillerson was fired very shortly after this visit. I suspect that Pompeo got the process started as the head of the CIA, possibly as a result of intelligence the CIA had on NK, and he was effectively acting as secretary of state while he was waiting to be confirmed on the NK issue.
But everything else he has done up to this point has been complete mockery..... 
