Someone is willing to gamble a significant amount of money on the idea of a shrunk-down Guitar Hero on the DS. BD&A, who make officially-licensed Nintendo hardware cases and accessories, will produce accessories for Guitar Hero: On Tour, meaning that they think the product is non-wacky enough (or lovably wacky enough) to sell -- and sell other stuff.
Two listings at Gamestop hint pretty strongly at their initial products: a $10 DS Lite Guitar Hero Stylus and a $20 DS Lite Guitar Hero Ruby Red Kit, which comprises "a glitter case, 2 system wraps, and a cleaning cloth." We assume they mean a DS Lite/Guitar Grip case that is glittery, and not a case for your glitter. They're saving that for Guitar Hero: Rip Taylor Edition.