[gcanyon]

It seems you're right -- I'm not in the "install other OSes" business, and I didn't know about the bootloader restriction. I was going off the fact that jailbreaks existed at some point, I didn't know that more recent iPhones have gotten harder/impossible to break.

And certainly, since the concept of hardware lockdown pretty much wasn't a thing twenty years ago, the Jornada probably puts up no intentional barriers.

I think the complexity issue holds -- it doesn't make it impossible, but surely it's easier to implement an alternative OS for something as simple as the Jornada. Although playing devil's advocate, the Asahi page only lists 8 people (compared to the 5 for the Jornada) so it can't be that much more complex. And it's irrelevant because of the bootloader thing.

It appears from some quick reading that the bootloader is a security technique -- that same lockdown that prevents alternative OSes also prevents malware. I understand if people disagree, but that seems like a reasonable trade-off to me.