How about a taxi or Uber-like app that connects passengers with advertisers via e-ink. Depending on who is driving in the cab, the car changes to a specific company's ad. In return, the advertisers pay for the ride or at least discount it for the passenger.
How it works:
An individual creates a profile, fills in his form, links his LinkedIn, Instagram, or Twitter, and based on his interests the app makes suggestions to advertisers on whether the individual is worthy of being a "mobile influencer" for them.
So if you are a fitness Instagram model, you'd get them coming out of a vehicle with your healthy food product. If you have a business person with a strong following on LinkedIn, the car would have a SAAS company advertising on it.