It is additional work but I believe something should be possible on iOS7 and Mavericks. If I remember correctly you will now be able to get the original purchas

It is additional work but I believe something should be possible on iOS7 and Mavericks. If I remember correctly you will now be able to get the original purchase receipt including the date of the purchase not just the receipts for the in-app purchases. If you can separate out some or all of the feature upgrades and disable them when the original purchase was before date of upgrade release unless an in-app purchase is made for the upgrade price. Won't this work? I realise that it doesn't come without effort to set it up and to test the software in two modes but at least bug fixes can go to everyone without two releases. Up to now I don't think there has been a way to identify when the initial app purchase happened.