Is there still a point to use AdMob? Has it been or will it be banned by Apple? Is there an third-party interface solution that allows me to switch between the services later on server side?
AdMob is limited by the terms of service in the analytics it can gather, but if that's not important to you, it's not banned.
Better to go with iAds. No one knows, apple releases an update and your application starts breaking. They are very much into it and for wiping out their competitors, its high possibility that they do it very soon.
Ultimately its your choice, you can use any.
An idea. What about using a combination of the two? So far, the story on iAds is that the fill rate is very low. Apple suggests moving the BannerView off-screen when the ad request is not filled (great idea). After moving the BannerView off-screen, why not move an AdMob ad into the void. Not sure if mixing ad platforms would cause poor user experience, but it might be worth considering.
Just a thought.
Andrew