Storyboards should have been multi-file from day one. Even if I didn't have issues with revision control, etc. I don't like the idea of a single corruptible file format encompassing the whole universe (all it takes is for Xcode to one day decide it can't open the file, and you lose everything?). This single-file risk happens with other GUI environments too (e.g. in Qt Designer it is quite easy to jam a lot of stuff into a single interface file; you have to go to extra effort to logically separate things into different frame classes or something so that they can live in different files).
