pyobjc-framework-Cocoa contains the API bindings for Foundation. A number of bindings are closely bound to the core bridge and should be in pyobjc-core.
NSDecimal (the C type, needed for the NSNumber proxies)
NSData (already has some bits in pyobjc-core, move all special handling there)
NSString, NSDictionary, NSArray: pyobjc-core already contains important parts of the binding; move everything needed for normal operation over.