Gentlemen, in the end, DK's position on the tier list is not determined by how good of a character he is. In fact, it is more determined by how popular of a character he is. While the two are not mutually exclusive (meaning that they sometimes intertwine, ex: popular fox was the best in melee), it is very important to note that tiers are determined by how often a character wins tournaments.
It all has to do with the metagame (if you don't know what this means, it basically means the way the game is played currently). If DK were one of the best characters in the game, but he was barely ever played due to his stigma as a "slow", "comedic", or even "tournament taboo" character, then he would be placed lower on the tier list simply because less people would play as him. The fewer the people who play as him, the fewer techniques are discovered for him, and the less involved he is in the metagame. If Lucario is a very bad character but is incredibly popular, then more players will enter tournaments with him, therefore more tournaments will be won by Lucarios, therefore he will rise on the tier list. The mutual exclusivity breaks here, because the more a character is played, the better he becomes thanks to new discoveries or studies.
In the long run, the more a character is played, the better he will be. In the short term, this means that if DK is not popular during the first year of Brawl, he will be low on the tier list, despite how great the few DK players are. In definitive terms, I iterate, tiers are determined by how often a character wins tournaments, and by consequence, partially by how popular a character is.
Basically, don't expect DK to be high on the tier list unless he becomes more popular. Remember that the early tier lists in Melee had Zelda as high tier, and after the metagame evolved, she was lowered. Things always change depending on the community.
Speculation as to whether DK will be Mid, High, or Low tier should not be simply determined by how good of a character he is. Besides the argument that I have just presented, we must take into consideration the fact that we the goers of this forum will be biased towards our big ape. Instead, speculation should include how popular he is and how great of a character he is.
When I combine those two, I don't see him being very high on the tier list yet. But please remember that I will give no importance to tier evaluations until more tournaments have been held. Because tiers are determined by tournament performance.