Dear Apple,
Please consider adding this option. Othewise storyboards are an anti pattern. They are responsible for both layout and navigation, breaking the first principle of OOP.
Apple - Why can't we import xib into storyboards?
An interesting request, but since forum posts aren't bug reports, it's best to file an enhancement request via the bug report link, below right, adding your report # to your thread for reference, thanks and good luck.
This isn't close to being true.
A storyboard — loosely understood — is a kind of aggregate file, or, from the point of editing within Xcode, a representation of a kind of file. In that sense, it's not an object, and doesn't conform to any principles of OOP.
A storyboard object, on the other hand, is an instance of class UIStoryboard or NSStoryboard, and is responsible for neither layout nor navigation. UIStoryboard and NSStoryboard are actually very simple classes, that do basically one thing: they manage the instantiation of storyboard scenes (which are instances of various other classes). That is precisely in line with the principles of OOP.
The difference between a storyboard file and a XIB file is mostly about the complexity of the object graphs they can represent, not about the functionality of any particular class of object.
Up to a point, you can already "import" the contents of a XIB file into a storyboard: you can copy the contents of a XIB file and paste them into a storyboard scene.