An API that is open to 3rd party launchers. Per the information that OW will be using their launcher to generate a lot of revenue. My thought is that this API should also push the current ad. To help ensure that 3rd party launchers are displaying the ad, a 3rd Party Launcher Certification should be given to launcher developers that display the ad. A token or something is in the transaction to indicate a sanctioned launcher, if no token the launcher can't access the api.
Users of the launcher should be able to get a reward for reporting on launchers not displaying the ad if it is found to be true. Like the way you can narc on people with the crime hotline and get paid.