I highly doubt that you're going to get a proper shell on the iPad.

I'm assuming you mean a shell into the iPad's own Unix environment. You could build something for iOS that works like Crouton does on ChromeOS just fine. (Just, nobody has done it yet, for some reason. The iPad Pro is plenty powerful enough to run VMs!)

I don't think it's as easy as crouton. There's no chroot or user namespace equivalent for XNU.

iSH does this by emulating Linux rather than virtualizing it.

Both Pythonista and OpenTerm on iOS are "good enough" for a lot of what I need, but it would be nice to have a proper shell. Even if it's jailed/locked to /private/var/mobile

No effect at all. Apple is unlikely to make this possible, and given the sandboxing of Apps on iOS a meaningful version of this for local resources outside of the App are prohibited.

Agreed. There are some basic terminals available on iOS/iPadOS though, with ssh and other capabilities, but I can't speak to how productive one could really be with them. I wholly expect to see a version of Xcode released on the iPad within the few years, though.

I use Blink[1] to Mosh to an EC2 instance where I use Jekyll, Vim, and Git to edit a static website that’s built and deployed when I push master. I can transfer images from my Photos library using the local shell, which I then resize on the VM.

I’ve heard people speculating about “Xcode on iPad within a few years” since Swift Playgrounds was released. Hopefully it’s closer now, but I’m still skeptical.

[1] https://blink.sh

On a similar note, I hope an iOS (/iPadOS) app is in the works for https://code.visualstudio.com/docs/remote/remote-overview

iSH is not affected, since it currently only touches files inside of its sandbox.