Ok. I had a big sarcastic response to this threat typed up, but I'll try some common sense.
Most people do not buy a system for one game. There are of course exceptions, but in general, people wait until there are multiple games they want for a system before they buy it. One game may be especially enticing, but there are almost always other considerations.
Think about how you buy your systems. Is there one game you buy them for? For me, no. I bought my XBox 360 because I wanted to play Bio Shock, Mass Effect, Dead Rising, and Devil May Cry 4. I bought my PS3 because of Heavy Rain, Infamous, Uncharted, Street Fighter IV (my friends played it on PS3), and others.
Few people are going to pay 360-410 for Donkey Kong Country, or Wii Party, or Mario 3D Land, or even Mario Kart. But a lot of people (about 6 million) played DKCR and I would assume a good deal of those players liked it. When they see a commercial with DKCTF they'll say "oh cool a new Donkey Kong game". Then, they're more interested in the Wii U. They look into it a bit more, and they say "hey that four player Mario looks really fun" and "oh there's going to be a new Mario Kart for this" and "oh a new Wii Fit. I need to get back in shape..." and so on. Then eventually, assuming they liked those Wii games, have the money, etc, they'll buy the system.
So, to answer the question, it depends what you mean by system seller. If you mean system seller in the sense that people are going to pay 350-400 dollars just to play DKCR, no. I'm sure that somewhere there is someone who loves DK that much, but those people are few and far between.
On the other hand, if you mean,"will DKC factor into the decision to buy a Wii U for many people", then the answer is yes. Just like all of the other sequels to franchises that people enjoyed on the Wii will factor into the decision to buy the console.