I would love that option, but even with Ahasi for iPhones you'll still need to deal with the horrific kludge that is the modern modem. Open source networking stacks exist but they're still extremely limited. Just look at how long it took for the Pinephone to receive calls, and they interface with the modem over a standard protocol like USB.
The ability to install your own OS would be a nice end goal, but at this pace it'll take at least another 10 years of government regulation before Apple would even consider allowing that.
It would create incentives to explore and benefit from those efforts creating healthy non-monopoly ecosystem.
It would likely create second market for their devices that Apple doesn't care about (because they don't release new iOS updates for old devices), it would create incentive for vendors to support open source through legacy hardware reuse (what is your hardware legacy reuse score as opposed to destroy-recycle-as-minerals score kind of thing).
We live in times where shoes have longer life span than many billions transistor devices which is mad, non eco friendly status quo where government should be stepping in instead of some cherry picked nonsense that will take endless decades to iron out and at the end of the day will make all parties simply unhappy.
The ability to install your own OS would be a nice end goal, but at this pace it'll take at least another 10 years of government regulation before Apple would even consider allowing that.