Another good option for replacing the ads would be to put appeals in place, things like the recent push for funding for the ebola hit areas in Africa, the appeals that followed tsunamis, famines, and other natural/humanitarian disasters, and so on.
Yes, that's also an excellent idea. The point is to allow people, per the quote I linked, to adapt the ad space to their own taste. Humanitarian appeals could be a good default. This could also solve the problem that some people complain about, that some pages have layouts built with ads in mind and become "uglier" when ads are blocked (not that I ever saw this actually happening).