Anticipating the success of a product is not an easy task. Human history is full of both successful and unsuccessful products. Although simple toys like the hula-hoop were a tremendous success, the swing-wing--a toy based on similar concepts--was not successful at all.
The Swing Wing was a toy designed to capitalize on the fun of moving your neck back and forth repeatedly. It was a big failure in terms of adoption, despite its similarities to the extremely successful, waist-moving hula-hoop (the preceding image was found from https://en.wikipedia.org/wiki/Swing_Wing_(toy), https://archive.org/details/swing_wing).
Every app starts from an idea, and you never know for sure if that idea will work in practice. Waiting until your product gets built in order to validate...
