At first glance this news seems awesome for consumers:
Finally my old iPhone 3G can download apps that I purchased after iOS 4 became obsolete! This should have been communicated to us as developers and the revenue channel for Apple.
Developers, on the other hand, should be ready for an onslaught of support requests they can do absolutely nothing about. We’ve assumed, since the beginning of Apple App Store time, that old versions were not installable by devices unless they pulled a backup IPA and installed it manually. We know this happens fairly rarely. Some of us put checks in the app to notify users of new versions in the App Store, but did we prevent the app from functioning? Probably not.
If we have a backend in our apps, we probably continued to support the old version for a while by versioning the API calls. Most likely iOS 4 is not even something we test against our API. Now imagine users turning on old devices and installing an ancient version of your app. Do we expect it to work? We knew that this was a scenario but now that Apple is allowing downloads of an old version it implies we as developers support that version. We really need the ability to issue point releases for a particular older OS if this is to be a viable option for users. Up until now we’ve been told to abandon old iOS versions fairly quickly.
Hopefully Apple communicates this change to us formally and gives us the tools to prevent bad app reviews and an onslaught of support requests we can’t do anything about.