A complete rebuild from the ground up. iOS 15 is just iOS 7 stretched over a larger area. 7 wasn't meant for 6"+ screens and many of its interactions and features are a fudge on modern phones. To this end:
1. All user interaction with the main OS confined to the bottom 40% of the display.
2. A screen-edge 'back' swipe replacing the current shortcut which is at the opposite end of the screen to your thumb (like Android)
3. A redesigned 'wallet' screen featuring control centre on the bottom half and cards at the top
4. Subtle bottom-up 'toast' notifications when the screen is unlocked in a
similar vein to webOS
5. The notification screen itself redesigned to sit to the left of the homescreen, an area of no use since we got go-anywhere widgets.
6. The ability to put icons and widgets anywhere on the homescreen instead of having them float to the top, away from your thumbs
7. An 'icon' widget where I can keep 2 rows of app shortcuts at the bottom of my screen but swipe through stacks of them like a widget stack, eliminating the need for multiple homescreens and keeping all apps within reach of my thumb.
8. The ability to customise double-tap and hold abilities of the power button thus opening iOS up to the use of Google Assistant or Alexa in place of Siri if you wished.
9. Complete control of all default apps
10. 100% support for game streaming apps without the need for a crappy web browser interface or Apple's insistence that the game testing that goes on at Xbox et al is somehow not up to scratch
11. NFC interactions opened up so I can scan tags and trigger different things
12. On-device photogrammetry API without needing a web connection
13. Full manual controls over the camera. This has been a sticking point for iOS for too long, particularly as alleged 'Pro' devices do not actually give the user
professional controls. Paying an expensive subscription to a developer like Halide is not a solution.
14. An always-on screen for OLED devices
15. Gesture controls for FaceID devices. Useful when your phone is sat on a desk or a charging stand. Apple brought the company that made Kinect for FaceID so it should be possible. Gesture control API for developers.
16. A redesign of all internal apps for the bottom 40% interaction area. All search areas etc at the bottom of screens.
17. Spotlight commands on the lockscreen: swipe down to start typing and see a list of things to do (send tweet, message person x etc) justy like
webOS 'just type'.
18. Siri API for developers so they can program back in shortcuts "Hey Siri, order me an Uber" etc
19. Quick settings to appear as a dock on the app switcher screen. This would be customisable. Swipe left on the dock to make this appear on the homescreen
20. British motorway junction numbers on Apple Maps. Without this simple addition its pretty useless for driving in the UK