Phones are also often paid for too. If you had a keyboard + screen + battery and could just clip your phone in that would feel like a pretty nice setup.

Bonus there is that it's one place for all your data.

Alternatively, on the data side I've been shocked at how cheap storage is now. I bought a 256gb usb stick shipped for £10. I've got tiny 4tb external drives. You can get terabyte microsd cards! It'd be pretty nice to have a setup where the device is intended to be blank and you just pop your data card in. I know it's more complex but not that complex for what would to me feel like a fairly sci-fi thing.