Marvelous Entertainment may be struggling with the Wii, DS and PSP (they recently broke into the HD market as well with Deadly Premonition and No More Heroes: Heroes Paradise. Very doubtful those were profitable). But going over to 3DS development is only going to take them to bankruptcy a lot faster.
The shareholders at Marvelous should just sell off their company to be honest. If you can't hack it on the DS and PSP, what other options you have? There needs to be a whole lot of consolidation in Japan (and in the west for that matter. Struggling Indie devs like Ninja Theory and Realtime Worlds are destined for bankruptcy). You have all these little companies releasing gazillions of niche Japanese games. Fans of these games can't dream of playing them all. So many are going to be overlooked and sell poorly.
