The people at My Nintendo News like the Pokemon Rainbow rumor, and here's one of the comments in response to those who oppose the rumor:
"Well black 2 and white 2 just came out basically, so why would you make it so that it would stop selling. To me it makes perfect sense. Its so they don’t kill of black and white 2 sales. While still mkaking EVEN more money with this game. I hope its real. I believe it 80%"
Here's the link to the article: http://mynintendonews.com/2013/01/07/pokemon-rainbow-for-nintendo-3ds-and-pokemon-wii-u-application-being-revealed-tomorrow/