I do believe many current iPhone users would be tired of iOS
I am one of those people. Why? After upgrading of you cell phone, you would still keep your old iPhone. Would you rather have an iPhone 4S plus Lumia 920/820 or an iPhone 4S plus iPhone 5? It's more like eat beef every day vs eat different kind of meat.
There are two assumptions underneath. 1. Lumia is a completely different product and it is awesome. 2. We don't see whole lot of difference between iPhone 4S and iPhone 5 (especially after you update your 4S to iOS 6)
My aunt and I both updated our ipads have regretted doing that. My aunt is having second thought on buying an iphone5 since she said ios6 downgraded her ipad3. Family is afraid of buying new ipad because ios6 might be install. We just purchased 2 ipods last month and glad we got it without the update. Mom and sister-in-law don't want to update their iphones. They said their iphone4s are better than iphone5. Other than the ios, they don't see the need for a longer screen because now they have to carry something longer.
Adding facebook and twitter as an app is okay, but intergrating into your OS is no difference than a tramp stamp. It devalues the iphone and ceo cant even see it.