It has an arm64 CPU. It looks like this will be the first cheap, easily obtainable and hackable (?) arm64 hardware out there. I'm writing the arm64 Go compiler. I wonder if it's feasible to start testing on this machine too (e.g. how open it really is, how hard is to get a sane working environment, etc).
You could jailbreak an iPhone 5S for a year now.
After I will have finished linux/arm64, I am sure someone else will do darwin/arm64 soon, and it won't be too difficult. Arm64 is difficult because I need to write a new compiler, but once we have that, adding another target to an already supported operating system is a breeze.
On top of that darwin/arm64 would never become an official port if it required a jailbroken device (same reason why there's no official darwin/arm, although that might change).