The first would be a pleasant photo of the two leaders together. The second would be that in their personal discussions that they find something in the other that could serve as the basis of some ongoing constructive relationship. And third, that Kim Dae-jung gets something tangible out of the meeting, most likely in the area of reuniting families divided by the war. It is far less likely that the two sides will make progress on security issues. These three modest accomplishments should be sufficient for each of the leaders to sell this initial meeting to their respective domestic audiences.
Greater progress can await subsequent meetings.
One should never refuse to talk to an adversary, even if doing so carries risks. The announcement of the upcoming summit is consistent with a variety of hypotheses about North Korean motivation and behavior, and there is no guarantee that it will not end in tears. Only time will tell whether the planned summit will open a new, more cooperative era in North-South relations, and by extension a reduction in tensions throughout Northeast Asia, or will simply mark another dreary iteration in the North Korean extortion game.