Designing UICollectionView cells in nib with Interface Builder (without storyboard)

The simple answer is no, this cannot be done. Think of a storyboard as a collection of XIBs. A XIB simply defines the facets of a particular view so that it can be constructed at runtime.

Regarding collection views and their storyboard implementations, it's important to understand that a storyboard allows for nesting of viewcontrollers and defining collection views with their XIBs because that keeps the fundamental paradigm of storyboards coherent. Since a storyboard is the means of defining the "story" or scene of an application it is only natural that it allows for the declaration of the reusable views for use inside a collection view.

The same cannot be said for XIBs because the fundamental idea behind XIBs is in reusability. This will allow a collection view defined in a XIB to have any cells used with it as long as the controller registers these classes with the collection view. This way you get the benefit of reusability as another controller can use the same XIB and register different cells etc.

So I think it would be far more confusing to allow for the declaration of the supported cells of a collection view inside a XIB since that breaks the single responsibility principle(if it can be called that) that XIBs aspire to.

Your best solution would be to define a custom collection view subclass that registers the relevant cells on instantiation, and then use this class in your XIB.