According to SamMobile Samsung’s current flag bearer, the Galaxy S4, as well as its predecessor is going to get a firmware update this October; bringing its OS version to Android 4.3 and is said to bring a few enhancements to these devices.
Moreover, the website claims that the Galaxy Note 2 will also get the same treatment, but at later time which they estimated to be around November or early December. Other candidates that are said to receive the updates are the two handsets (Mega 5.8 & 6.3) under Galaxy Mega lineup.
Of course, as you might expect, the roll out date may vary from region-to-region and from telco-to-telco. As such, it’s best to not get our hopes too high and just let it take its course.