NanaOn-Sha's Masaya Matsuura has said developers in Japan are getting a bit concerned about the longevity of the DS and the audience to which it appeals.
He reckons younger gamers are cautious when it comes to new software, and titles aimed at old duffers aren't having the same impact as they did when DS first launched.
"Some people have said already that the DS software's bubble has burst," Matsuura told Gamasutra.
"We have to keep increasing the chance to make more unique titles, but for us it's getting much more difficult because the game market - especially in Japan - is still very conservative.
"Many people know that the DS has very unique titles, like Brain Training or something like that, but it's not for younger-aged market. It's kind of older people, like me."
The more developers jump on the 'training game' bandwagon, the more sales of such titles dip, said Matsuura.
"[One company I know has] some kind of learning type of game. The first one sold over 200,000, but the second one is 8000," he observed.
"So these kind of things are going to happen."
Not to Matsuura with a bit of luck. The developer may have made his name with PaRappa the Rapper but he's also enjoyed commercial success with the Tamagotchi Connection Corner Shop games for DS. Shame they're rubbish. His next project sounds much more promising - it's a music game for Wii being developed in partnership with Rodney Alan Greenblat, the artist who helped create PaRappa.