At least for companies that recognise they have a problem, and want ideas for how to solve it, such a market already exists - Innocentive https://www.innocentive.com/ar/challenge/browse

This includes various classes of challenge, including the Ideation Challenge:

"An InnoCentive Ideation™ Challenge is a broad question formulated to obtain access to new ideas, similar to a global brainstorm for producing a breakthrough idea or market survey which may include ideas for a new product line, a new commercial application for a current product, or even a viral marketing idea to recruit new customers. Ideation™ Challenge submissions are typically about two written pages, and Seekers receive a non-exclusive, perpetual license to use all submissions."