NSFileWrapper is really convenient, but has a lot of pain points. Here's my design for a replacement.

GBSFileWrapper.h

// There's a lot that bothers me about NSFileWrappers:
// * Directories are mutable, but regular files and symlinks aren't.
// * You can't change from one type to another.
// * ...but the -readFromURL:... method can violate both of these rules. Probably.
// * Wrappers include a .filename, but this is only relevant to their containing folders.
// * Wrappers include a .preferredFilename, but this is only relevant to the folder they're being added to, and doesn't matter after being added.
// * There's no way to replace a file wrapper in a directory, except by removing the old one and then adding the new one.
// Here's how I would design a file wrapper replacement.

typedef NS_ENUM(NSUInteger, GBSFileWrapperType) {
	GBSFileWrapperTypeUnspecified,		// contents is nil, -writeToURL:... fails
	GBSFileWrapperTypeRegularFile,		// contents is an NSData
	GBSFileWrapperTypeDirectory,		// contents is an NSDictionary
	GBSFileWrapperTypeSymbolicLink		// contents is an NSURL
};

// I'm not going to specify the reading/writing options, because they don't really matter that much.

@interface GBSFileWrapper : NSObject <NSCopying, NSMutableCopying, NSCoding>

// Designated initializer.
- (id)initWithContents:(id)contents resourceValues:(NSDictionary*)resourceValues;

// This would probably actually be implemented with a private subclass to allow for lazy loading.
- (id)initWithContentsOfURL:(NSURL*)URL options:(GBSFileWrapperReadingOptions)options error:(NSError**)error;

@property (readonly) GBSFileWrapperType type;
@property (readonly) id contents;
@property (readonly) NSDictionary * resourceValues;		// Uses NSURL constants

- (BOOL)writeToURL:(NSURL*)URL options:(GBSFileWrapperWritingOptions)options error:(NSError**)error;

@end

@interface GBSFileWrapper (SerializedRepresentation)

- (id)initWithSerializedRepresentation:(NSData*)data;
@property NSData * serializedRepresentation;

@end

@implementation GBSMutableFileWrapper : GBSFileWrapper

@property (readwrite) id contents;
@property (readwrite) NSDictionary * resourceValues;

// These only work on directories
- (void)setChild:(GBSFileWrapper*)child forName:(NSString*)name;
- (void)removeChildForName:(NSString*)name;
- (NSString*)addChild:(GBSFileWrapper*)child withPreferredName:(NSString*)preferredName;

- (BOOL)readFromURL:(NSURL*)URL options:(GBSFileWrapperReadingOptions)options error:(NSError**)error;

@end