If you want self-hosting for everyone, then I suspect you’re gonna have something like a console – a self-contained box that requires virtually no configuration.
So something like a Synology NAS, I guess.
And even that is not for the masses. It’s good, it’s for the medium savvy folks, but it will never be for my wife - or for my mother!
I suppose that that’s an “appliance-like computer” though I was thinking more of general-purpose hardware that takes software modules.
Like, think of how you install a game on a console. Maybe you set up your account at the beginning and plonk in a wireless password, but beyond that, there’s no further essential configuration for the thing to work. Same kind of idea. You get box, do initial minimal setup. After that, you install software modules, and they have no more configuration involved.
If more configuration is required, then it’s just not going to be something sufficiently accessible for everyone to use.
That’s probably not what the typical user on this community is looking for, but I think that that’s probably what would be required if one wants everyone in the public to be able to self-host.