It's a stretch to call it unneeded, being able to communicate over the cellular network is pretty much the definition of what a mobile phone is, if you remove that it stops being a phone. In that sense running the phone with any system is optional too since you can always use it to weigh down some papers on your desk ...
So? Apple made such a thing into a product years ago. It was called iPod Touch.
Pinephone may have a phone in name, but it's basically a neat little SBC with an integrated touchscreen and battery, and bunch of other peripherals, and can be used for anything you like.
