UICollectionViewDropCoordinator api is broken since beta 4 and the sample app from WWDC showing how to implement drag and drop in collection views also doesn't compile due to this api change.
UICollectionViewDropCoordinator used to have a method -[dropItem:toPlaceholderInsertedAtIndexPath:withReuseIdentifier:]. But in beta 4 this was replaced with -[dropItem: toPlaceholder:] with placeholder being an object of type UICollectionViewDropPlaceholder but there doesn't seem to be any way to get such an object. It's superclass has an init method that takes a reuse identifier but not the collection view in which this reuse identifier was registered hence doesn't seem correct and useable and in any case if you try creating such an object you get link errors.
I've written about this when discoveritng this in beta 4 and was told beta 5 was going to fix this, but that hasn't happened as far as I can tell. Anyone figured out how to use the modified drop API or know if Apple are planning to fix this?