The iPhone already doesn't support USB 3.0 speeds, or video out from the port so nothing would be lost.
And the data rate of the cable has no impact on it's power delivery capability. I have USB 2.0 speed cables capable of doing 240 watts. Plus the iPhone already does USB PD, just through the lightning port. https://lemmy.world/pictrs/image/12152bd5-5977-4cf3-9dd5-c302ca78462b.jpeg
USB C is already a mess, and plenty of Android devices don't support USB 3.0 speeds either. Apple changing to USB C port changes nothing except for the literal receptacle.