iOS 7 changed the icon shape already, they aren't going to change to a round icon, there are just a lot of them used in the UI (for contact pictures for instance).There's quite some chatter on the inter webs about Apple possibly holding back on same major new features in the iOS GM. As mentioned, 5C's are already assembled and on US Soil, although Apple has not released a GM to devs. With the talk of slomo camera features, finger print scanning software, etc. this theory is pretty much validated.
The latest conspiracy is Apple may be changing App Icons to circles. Whispers that the grey circles could be the new home button image, and all app icons become circles to match. Macrumors did mention this in an article ran a few months ago (anyone wanna dig that one up?) I attached a picture for some further explanation.
Image
Think, Circle app icons sure would be interesting. Dial screen, Lock screen, and Safari/iTunes/App Store icons all lend credence to the conspiracy theory. Also, for Apple's new icon design template, the geometry sure is circular.
Now before you throw this out the window and damn me in future posts, just give it some thought. Apple has a GM (on the 5C) but not publicly available to devs - yet. There's always those tidbits that are saved until the hardware release, I don't think we will see one until the 10th after everything is announced. There is definitely features we do not know about, and aren't supposed to know until September 10th.
http://blog.manbolo.com/2013/08/15/iOS-6-vs-7.gif