"However, if the foldable iPhone is intended as a phone that can become a tablet when needed, like the Galaxy Fold, it's certainly possible the price could well exceed those of Apple's more conventional smartphones."
That won't be happening anytime soon with iOS, especially since Apple still encourages its developers to make separate iPhone and iPad apps. Plus continuity wouldn't work when switching from an iPhone to an iPad on the same i-device that folds like that. Besides today you would have to load both versions of the same app on the one device. I will go out of my way and say as a developer you will NOT see a device like that from Apple, if ever, unless Apple does a complete revamp on its app ecosystem. Now Apple could have a foldable that stays as an iPhone with only iPhone apps, like the Moto Razr or Galaxy Flip. But I will put that guarantee on that you will NOT see a Samsung Galaxy Z Fold, or Mate X Fold type devices for a very long time. Those devices work because Android and Google encourage their developers to make one app that works as both a smartphone app, and a tablet app.