I wonder why that doesn't happen today. It's technically accessible. I've seen a blimp with a banner in the past once. No audio. What stops ad people from jumping at this medium?
It's probably against the law to annoy residents with audio ads from blimps and for a good reason.
I bet rednecks would shoot their rifles at would be audio ad blimps passing over their property without thinking twice - like they do now with drones. And I don't blame them, because I'd do the same any day.
I'd buy a rifle for that reason myself. Or revive my high-school hobby of building solid fuel rocket engines. I'm just curious what stops ad blimps from appearing in big cities.