Here is a portion of a CNet interview with RedOctane Cofounder Charles Huang:
CNET.com.au: What can you tell us about Guitar Hero III DS?
CH: We are working on that. We’re exploring a lot of things. We’re hoping to really bring the experience to the DS and to do some very, very different approaches. We’re working through a lot of engineering issues with Nintendo. I actually came from a set of meetings with them last week about this. While the technical path hasn’t been set yet, we intend for this to be a very unique experience just like Guitar Hero was on consoles. This will play probably unlike any other DS game that has come out, and at this stage, that’s all I’m afraid we can talk about until we have the engineering paths laid out with Nintendo.
CNET.com.au: Are there any plans to have a custom DS peripheral?
CH: That is definitely one of the options we’re exploring. The DS peripheral is very intriguing to us. It’s an integral part of the Guitar Hero experience, so as much as possible, we would like to keep it within the experience as long as it makes sense and it plays well. And we can do it on the DS where it not only makes sense for the title, but also for the way people like to interact with the DS. It needs to be affordable and it needs to fit within the environment that people normally play DS games in, but central to it all, we are exploring ways to get peripherals on a DS game.