As an App Developer, every new release of iOS means a scramble to make sure my apps are compatible, and usually they are. But once in a while, Apple changes things just enough that old apps need to be tweaked to work with the new operating system. Making a living on the App Store, while difficult, is possible, but you have to keep your apps updated and add new features as Apple adds capabilities. The sad fact is, not every developer does that. Indeed some developers will be probably have apps in the App Store that simply won’t work on iOS 8, and never will. The developers may have shut their doors, and there may be no plans to fix incompatibilities.
As an end user, the safest approach may be to sit back and wait for the app reviews. Early adopters will make it clear, through their reviews, if an app is broken. Before you upgrade to a new phone, or to iOS 8 on your existing devices, take some time to make a list of the most important apps you use on a daily basis and watch the reviews for those apps, once iOS 8 is out. Be sure to check with family members if you share your iOS devices. Trust me, you don’t want the kids to complain because their favorite app isn’t compatible with iOS 8!