The AdEx protocol is intended mainly for display advertising, however its use is not limited to that. It can be applied to a number of different use cases - for example influencer marketing; content micropayments; affiliate marketing; product placement; and so on.
The revenue model could be CPC, CPM, CPA or time-based ad property rentals. This makes the protocol usable for physical world advertising (billboards, point-of-sale advertising, guerilla installations, etc.) as well.