Since the Wii Vitality Sensor was revealed back in 2009, Nintendo has been pretty quiet about how the peripheral was coming along. Nintendo president Satoru Iwata confirmed work was still being done on the Vitality Sensor but there's trouble making the device work with some people.
Because our human bodies have diverse biological differences, the Vitality Sensor hasn't been able to detect pulse and other body signals from a good chunk of users. Nintendo is aiming to have the device be usable by virtually anyone though working out the kinks has taken a long time.
Iwata admits this problem has been tough to overcome but he believes the Vitality Sensor has potential and wishes to continue working on it. Iwata did not provide a possible release period for the Vitality Sensor.