Not exactly what you're talking about, but I've seen a few RaspberryPi + iPad + External Keyboard setups where they either use the iPad as an external display or VNC into the Pi from the iPad. IIRC you can power the Pi via USB C -> PoE on iPads with sensible ports on them, so you don't need an external battery or UPS.

Again, not what you actually want (I share your pain/longing), but damn if it isn't starting to get close.