There's a sizable contingent of iOS users who opted to stick with iOS 6 over iOS 7 due to the drastic visual changes introduced with the operating system update...
No, not really.
iOS 7 adoption is at >80% of compatible devices. Of those remaining I doubt many are consciously choosing to avoid iOS 7. Most are probably just lazy and haven't bothered to do the upgrade. That leaves just a small fraction of users who are clinging to iOS 6 on purpose, and only a subset of them might be using FaceTime. So in all, this impacts a small small number of users and the fix is easy. So deal with it.