After updating from Yosemite/El Capitan, Xcode 7.x/8.2, and RM 4.11 to a fresh install of Sierra, Xcode 8.3, and RM 4.18, I was surprised that none of my previous OS X projects run with the new stuff. They build OK, but crash immediately since none of the outlets and actions seem to be getting connected (every UI object is listed with 'failed to connect' or 'could not connect'). I don't use any gems to manually build my interfaces, I've had no problems using Interface Builder (well, other than the regular Xcode silliness).
Basically I built an Objective-C template a few years ago that includes .h and .m files stashed away in the vendor folder, and an .xib file in the project resources folder. The files are all linked together in an Xcode project, with the File's Owner set to the window's class, which inherits from NSWindowController. I can edit the files from my project editor, and/or run the Xcode project to tweak the interface.
I don't have any settings in the Rakefile, the .xib gets compiled by being in the resources folder, and by setting my app controller class to inherit from the NSWindowController, everything just worked. Did I miss some changes, or was I just lucky with the way I was doing it before?