checkra1n (current jailbreak for devices with A10 or older chips) is based on a BootROM exploit, so thankfully I can keep my iPad on newer iOS versions and remain jailbroken.
The 3G had a commodity Samsung CPU core and 'off the shelf' third party subsidiary components, the drivers for which were available. Modern Apple custom in-house chips not so much.
Yeah, I sunk a few hours into trying to get Docker running on a jailbroken iPhone. It’d be awesome if all the arm work done for Raspi (et al) since the last hey day of Jailbreaking, could be easily ported to arm64 (Darwin)
It is possible, and I believe a few of the developers of checkra1n/some of the community has expressed interest in running Linux. Whether or not it happens who knows.