They (well, Shin Adachi is) are currently playing around with a new prototype car, according to my sources, in the end this should be the new YZ4 (and that's all I can say for now). But, release date is unknown. Probably a belt-driven car.
If you look closely to the front.. It's all wrapped up. So transmission seems to be open (and the car was damn silent). So possibly testing with belts.
As I told back in December, this could happen, a new belt driven car. My guess? A high traction 4WD car. Not even close to the B-Max4 III.