They will have to work a little harder this time to get public acceptance of Kim Jong Eun as leader, for 3 key reasons that I can see: 1) Jong Eun is much younger, at 26, and has had much less time to be groomed for succession than his father had; 2) Jong Eun is the third son, with an older brother and half-brother who are both alive and healthy; traditionally Korean royalty (as well as many modern South Korean companies) have given preference to the first-born son unless there is something seriously wrong with him (Kim Jong Il was himself a first-born son) 3) the economy is in much worse shape than it was in 1994 when Kim Jong Il unofficially-officially took over, and reports indicate that people have begun to wrap their heads around the concept that a son can have faults even if his father was the Most Perfect Human Ever Born.
Nonetheless, with the reports of these birthday celebrations, it seems that North Korea has finally committed to Jong Eun in a way that would be very difficult to back out of. In further confirmation, I saw an article in the Daily Chosun newspaper today claiming that the Japanese botanist who created Kim Jong Il's flower hybrid, Kimjongilia, has already created a new flower for Kim Jong Eun. If true, they are indeed moving ahead quickly with the succession propaganda.
North Korean publications dwell a lot on these flowers, praising them as great scientific achievements and symbols of international admiration for the Kims. The first, Kimilsungia, was reportedly a flower hybrid developed in Indonesia which Sukarno decided to name in honor of Kim Il Sung during his visit to the country. Subsequently, in 1988 a Japanese botanist developed his own flower hybrid and named it Kimjongilia. I've heard that North Korea's botanists run themselves ragged each year trying to get this flower to bloom in special greenhouses in time for Kim Jong Il's birthday on February 16th. I can only imagine how they must be privately grumbling at the prospect of having to get this new flower ready even earlier next year by January 8th.
Photo of Kimilsungia display courtesy of songun-blog