I'm now close to releasing a major upgrade for an iPhone app, but these upgrades aren't going to be sustainable for me without paid upgrades (I don't want the new features to be IAP features)
In the long run, this will also benefit customers because paid-upgrades will help developers add more features to the app. Users who want the new features can pay for the upgrade. Users who don't want to pay more can stick with the older version of the app (and hopefully the app store will make it possible for users to re-install older versions of the app).