I sent an e-mail yesterday to Nintendo regarding this very subject, here is the reply they gave me.
I said "There have been some rumours going around that Rareware was going to be developing for other consoles than Gamecube...is this true??? Please turn the lights on for me.
Gamer."
Here is what they said " As far as I know, Rare will continue to make games exclusively for Nintendo video game systems."
They didnt say too much but hopefully that is true, although, he used the words, "as far as i know" ... that isnt too reasuring.
Well, i personnnally hope that it stays exclusive for Nintendo.