It's really hard to get old iPads and iPhones to do anything at all, which is a shame, because iPad hardware is actually fantastic and would still work great with a replacement OS.
At least in 50 years we should be easily able to crack all the signing keys etc so we can boot old software and write new software the passes auth checks on old hardware.
I’m sure people will be able to run it on their optical toe implants or whatever. I grew up hacking assembler as a kid in the 8086 dos era and am still amazed to see it run in a browser window like it’s nothing. Entire Linux systems run in the browser now.