I'm still not entirely convinced the reasons the DS is selling so well is the touchscreen and the dual screens. I'd attribute it primarely to brand-recognition and software support, rather than the hardware specific features its offering. As a result, I'm not entirely sure Revolution will do much better than GameCube.
The potential is there for it to do better, but on the other hand, it could also backfire by drastically changing the concept of which has proven to sell quite well and expand (the path consoles have went the last 3 generations and expanded the market). On one hand, I could see Nintendo loosing even more customers that will be heading off into the Xbox/PlayStation camp looking for something more traditional, while I could see others go to Revolution for that exact reason. Given I'm still not sure what we can exactly expect from Revolution, it makes it quite a tough on to answer or even predict. What I do see though is that Revolution could do quite well entirely on consumers that are looking for a cheaper, innovative 2nd console that has offers something quite different. I see this far more likely than people buying a PS3 AND a Xbox360, given both are more or less going to offer the same experience, similar type of software and appeal to more or less the same market.