I went the classic way. Just use single localized images and set up your plist correctly. The easiest way is to use one asset catalog, set everything up. Then open the application bundle and copy the correctly named files + the correct info.plist entries. (And of course remove the assets catalog afterwards) Result looks like this:
Info-plist:
Launch images filenames:
(I needed all iPad orientations/sizes + all portrait iphone sizes + 7.0 specific sizes)