Here's what we know for certain about the upcoming September 10 event:
A new Apple product of some kind will be announced. Probably an iPhone.
Here's what we suspect will be announced at the September 10 iPhone event, based on the few credible rumors skimmed from the meniscus layer of a deep ocean of BS:
The next-gen iPhone will probably be called the iPhone 5S. With few exceptions, it will look externally identical to the iPhone 5. It will likely have a faster CPU. It may have an improved camera, including a dual flash. It may or may not have a fingerprint sensor.
Alongside this, the iPhone 5C is likely to be announced. This is an iPhone with a plastic backside that will be available