I was in the mobile billboard industry back in 1999 and it was a hot market because it was new, as is the case with all advertising. We see trends in advertising, but what was hot yesterday does not mean it will be hot tomorrow.
I shifted to auto wraps for a couple years, but like all advertising, it loses impact once everyone is doing the same thing. Now I use Mobile LED Signs in back windows of cars and trucks for the lowest cost in your face advertising medium known, and it works.
As to your idea, no doubt, it is a good concept as mobile advertising is one of the least costly and targeted means of advertising. I promote recession proof home based online businesses, so I can park my car strategically in front of my target market and let my custom messages do the selling, no matter where I drive or park, I make sales, and if I set up at events by main entrance at job fairs, home improvement or business opportunity conferences, and conventions, as example, I make more sales than any other medium I have used, and I have used them all.
Your concept would be great for riding around college campus promoting local restaurants with a special two for one sale or whatever, this is what businesses are looking for now, cheap in your face advertising, especially in a recession. Take not, when I was using special sign trucks and tow behinds, watch out for windy days, even more so on a bike. lol
Success to all,