Deep mutable copy category method of NSDictionary (ObjC)

Deep copy

- (NSMutableDictionary *) mutableDeepCopy {
    NSMutableDictionary * returnDict = [[NSMutableDictionary alloc] initWithCapacity:self.count];
    NSArray * keys = [self allKeys];

    for(id key in keys) {
        id oneValue = [self objectForKey:key];
        id oneCopy = nil;

        if([oneValue respondsToSelector:@selector(mutableDeepCopy)]) {
            oneCopy = [oneValue mutableDeepCopy];
        } 
        else if([oneValue respondsToSelector:@selector(mutableCopy)]) {
            oneCopy = [oneValue mutableCopy];
        }
        else {
            oneCopy = [oneValue copy];
        }
        [returnDict setValue:oneValue forKey:key];
    }
    return returnDict;
}

This is so nice! Could it be even nicer, to support the equivalent of mutability-options in NSPropertyListSerialization? i.e,

typedef NS_OPTIONS(NSUInteger, NSPropertyListMutabilityOptions) {
NSPropertyListImmutable = kCFPropertyListImmutable,
NSPropertyListMutableContainers = kCFPropertyListMutableContainers,
NSPropertyListMutableContainersAndLeaves = kCFPropertyListMutableContainersAndLeaves
};

so mutableDeepCopy method can receive the option, and selectively make (deep) mutable copies only to containers, but NOT to the "leaves" (e.g. NSData, NSString, NSDate, NSNumber etc. ? What's the best way to go about it?