Right, which is why I added the bit about salting the URIs before encryption. The salt could be per request, per session, or rotated after some period of time (say once per day). If only rotated once per day, it would still thwart ad blocking, but have less of an impact on caching. It would turn into an economic question of whether the extra ad impressions are worth the extra bandwidth.
The idea is that the ads would be served from the original host. Combined with encrypted URIs and the ad resources become indistinguishable from content resources. Thus thwarting blocking. As others have pointed out, yes this evil trick is incompatible with existing ad networks (which use their own domains). But it wasn't my intention to put forward a viable idea. Just an interesting one (namely, ciphering URIs to prevent blocking).
