Rare's official spokesperson spoke about the improbabilities of a new Killer Instinct title:

"Okay, here it is. Sword sheathed, hands on the table. There are all sorts of reasons that KI3 has yet to be attempted: in addition to holding back further development until we feel we can really bring something new and worthwhile to the genre, one of the main reasons that there haven't been any recent additions to the series is that all of the key people who were involved in the creation of Killer Instinct have been working on different projects. There's also the matter of knowing which way to take the franchise: some people prefer one installment to the other, some champion 2D while others insist that only 3D will sell nowadays, etc. It wouldn't be a straightforward undertaking in any sense of the word: opinion is doomed to be split on the final decision. Nevertheless, we haven't abandoned the franchise."

There you have it... there may come a KI game to the GameCube. But not yet.

We will keep you posted!