If that system preference ever gets added I want Apple to continue selling a version of iPhone that doesn't have it, with no way to enable it and with a promise to never add it in a future update. I consider not being able to sideload software onto an iPhone to be an important feature! I like knowing that if someone malicious with moderate but not extraordinary technical ability gets ahold of my unlocked phone they are limited in their ability to compromise it in a way that persists through a restart. I.e. what any border guard can demand on entering any country I can think of. If I used an Android phone I would destroy it if it left my sight unlocked and I didn't know what had happened while it was away.

I have root access to plenty of hardware devices. I don't need root access to every hardware device I own. What am I going to do with that capability on an iPhone, sideload Fortnite? No thanks, this is the device I use to check my email.