No way. iPhones don't exactly allow bootloader unlocking to begin with, but even if you could, it would be in no better state than Asahi on the M1 Apple computers. Every driver would have to be written from scratch.

Pixels are a good platform for custom ROMs because until the recent drama, you could literally just build AOSP as-is and use it. So the GrapheneOS team only really need to focus on their changes to the OS and their apps and none of the drivers and modem interface and all that. That's also why GrapheneOS runs so well on it: Google provided everything, it just works.

iPhones would be the absolute worst phone to develop for: zero support from Apple, no drivers no documentation, no nothing. Not even a Linux kernel! At least for Android, the Linux license forces manufacturers to publish the source code, so at minimum you start with something that should boot and contain all the stuff to talk to the hardware already, just need to wire it in with userspace drivers. CPU manufacturers like Qualcomm also provide a fair chunk of the userspace drivers open-source too, so you can just pull that and have audio and video working.

Not impossible, but definitely really hard and impractical.

iPhones have locked bootloaders, and that likely will never change.

Apple would never agree to it, and they have no reason to.

iOS is a stripped down version of macOS, which is certified UNIX, whatever that means. They also claim to safeguard your privacy, though I'm not sure they've ever proven it. Quite the opposite, I think they've unlocked iPhones, handed over iCloud data for law enforcement, while denying grieving families the same privilege.

I think the best outcome would be for some privacy fanatics with deep pockets to purchase a smaller OEM that already has manufacturing down. The problem they will run into is how to fund it and how to compete, not only with iPhone and the big Android OEMs, but with the smaller Android OEMs that have the same stated goals, to protect privacy. What that might look like is a phone with specs a couple years out that costs maybe a little less than the big names, with the speculation that if enough people buy it, they will support it, but if not enough people buy it... they won't.

Why would using Apple's walled garden be a solution to Android becoming a walled garden? I can't understand why this sentiment of moving to use Apple comes up so often lately.

how feasible is it

No.

I mean... if you are love swimming upstream, yes, go for it!

Lmao what

Keep your eyes on Linux phone developments. That's likely where the future lies for any semblance of privacy on a cell phone.

It would eat away at Apple's claims of "privacy" on iOS.