So fun story, notification observers are invoked on the thread from which you send the notification. Also I like GCD.

NSNotificationCenter+Concurrency.h

#import <dispatch/dispatch.h>

@interface NSNotificationCenter (Concurrency)
+ (void)onMainQueuePostNotificationName:(NSString *)notificationName object:(id)object;
+ (void)onMainQueuePostNotificationName:(NSString *)notificationName object:(id)object userInfo:(NSDictionary *)userInfo;
+ (void)onQueue:(dispatch_queue_t)queue postNotificationName:(NSString *)notificationName object:(id)object;
+ (void)onQueue:(dispatch_queue_t)queue postNotificationName:(NSString *)notificationName object:(id)object userInfo:(NSDictionary *)userInfo;
@end

NSNotificationCenter+Concurrency.m

#import "NSNotificationCenter+Concurrency.h"

@implementation NSNotificationCenter (Concurrency)

+ (void)onMainQueuePostNotificationName:(NSString *)notificationName object:(id)object
{
    [self onQueue:dispatch_get_main_queue() postNotificationName:notificationName object:object];
}

+ (void)onMainQueuePostNotificationName:(NSString *)notificationName object:(id)object userInfo:(NSDictionary *)userInfo
{
    [self onQueue:dispatch_get_main_queue() postNotificationName:notificationName object:object userInfo:userInfo];
}

+ (void)onQueue:(dispatch_queue_t)queue postNotificationName:(NSString *)notificationName object:(id)object
{
    dispatch_async(queue, ^{
        [[NSNotificationCenter defaultCenter] postNotificationName:notificationName object:object];
    });
}

+ (void)onQueue:(dispatch_queue_t)queue postNotificationName:(NSString *)notificationName object:(id)object userInfo:(NSDictionary *)userInfo
{
    dispatch_async(queue, ^{
        [[NSNotificationCenter defaultCenter] postNotificationName:notificationName object:object userInfo:userInfo];
    });
}

@end