This is an excellent idea. Steemit is likely to have the highest take-up and the biggest impact in poorer countries. Furthermore the ad-rates are likely to be very very low on something like Facebook.

Billboards may be more effective at intersections and stop-lights, like the most recent New Zealand post. But I think the money would go much further in somewhere in Africa, than there.

Anyway - let's see what happens. I support your idea and it's a smart move. Even if this post doesn't get any traction - keep persisting, here and in the Steemit chat room. You'll get support.