By garner public support I mean that the North Koreans may not support him as much as they did his grandfather and father because he has little to show other than the fact that he is a Kim. When Kim Jong Il first became the ruler of NK a lot of people speculated that he might not reign comfortably since the people didn't like him as much as his father. Kim Il Sung was the great war hero who saved the North Koreans from the Americans while Kim Jong Il had accomplished little in comparison. While the North Koreans still worshipped Kim Jong Il fervently (proving the speculators wrong) I don't think the North Koreans loved him as much as Kim Il Sung. Now a teenage brat who Kim Jong Il had kept sheltered for the past two decades of his life is going to take the throne. If you were North Korean wouldn't you, too, be a little skeptical about little Kim's ruling abilities? Like I said the halo of the Kim Dynasty might be the only thing keeping him in power once he does and if he doesn't prove himself quickly (either as extremely harsh or exceedingly "benign") we may see the inner circle turning on him just as fast.
The thing is, "Kim the 2nd" wasn't that much of a hardliner in reality, he did tried limited reforms but they all ended up canceled and half-arsed affair because of his insecure personality. DPRK kept the nation in a largely lock-down state, replaced contemporary religion with the "Kim cult" that'd surpass Mao's era China, and when that doesn't work iron-fist approach...
Still, domestic and international situations that'd face "Kim the 3rd" would be more grim - largely unknown even by the N.Koreans, next to nothing to show his worth other than his bloodline, no more Soviet backing, China only willing to keep the DPRK at a limbo state (without China's aid keep poring in, DPRK can't survive more than a month) for all its worth, tougher international sanctions, hardline eastern neighbours, hungry population, even the army doesn't get their full rations (their parades look grand and all, but can't hide the fact that their soldiers weren't as nourished as they should have been)...any reform would've to scrap the support beams that held up the regime (the "Kim cult" and lock-down state) - a vacuum of beliefs can't be filled with money as the new religion, as China have proved over the last 30 years.
That leaves the oldest trick in the book - risk a war to exploit the patriotism that the regime worked so hard to cultivate over the half century. Unlike the last 2 failed example - Argentina's military junta or Saddam's Iraq - who did so without proper preparations, DPRK tailored it to their strength and limitation for so long:
- very well prepared artillery positions all along the border of the DMZ, and the numbers to go with it - in terms of artillery warfare, it's as important in range, volume, surprise as to accuracy, which they got the first 2 covered for sure; surprise would be harder to attain but the warning time the S.Korean and Americans would've is still short enough to make it worth the while.
- air power is irrelevant to DPRK for this part their assets are totally outgunned and they know it, but if their ground assets could pull the punch quick enough they can gain some ground before the S.Korean and Americans can scramble significant air assets to dislodge them
- air defense wise what the DPRK got is either hopelessly outdated or untested in actual conflicts, but neither the Americans faced any enemy over since Vietnam that process significant modern air defense
- likewise would be their navel assets, which would be the lack of it to be accurate, all would depends how fast the S.Korea and American mobilize in actual combat situations
- in terms of ground warfare, DPRK is inferior in terms of hardware, even their best is behind the west by at least a generation or more, infantry seems to be pre-modernized China standard of equipment, not to mention Korean landscape isn't favor large armor formations, known and usable corridors are marked and "prepared" by the S.Koreans for just such an event - the only advantage is numbers and determination, but this isn't the 1950s anymore, tricks that the Chinese used to great effect won't work so well in the modern age. That said, this'd be real proving ground as to how much technology can make up for the lack in numbers.
- the spec-op sections of DPRK would be an interesting card to play. They've their fair share of records in espionage and infiltration, however the S.Koreans already caught on and displayed their abilities in countering them.
Yet, what the world are more interested would be this scenario: what'd it be if the DPRK implode before "Kim the 3rd" could stabilize his reign? What'd the major powers in the region do in such a case? What'd be the role of China in this? Losing DPRK probably means the "Asia-NATO" have their guns stationed just opposite Chinese border, and from there:
1. effectively blockaded Chinese's North Sea fleet homeport
2. several China's key industrial bases (to be specific, naval and aircraft productions) under threat
3. Beijing comes under even more threats from assets stationed just outside of its border, when there's no more a DPRK to provide a buffer zone.
We all know why China keep such a troublemaker around, to maintain a buffer zone more than to spite the Americans, so would China intervene? Or whoever seized power seek warmth and protection from?