People were asking if the next 9.7" iPad would support the Pencil and Keyboard. If Apple can support that on a smaller form factor, I don't see why they can't support True Tone on a larger form factor....
I wonder if an app could make a poor man's true tone with information from the front facing camera. If you didn't want to use the light reflected off your face, I suppose you could tape a small piece of paper over the camera to make it like a light meter of sorts.
Night shift is different. Night shift adjusts the colour of the screen based on the time of day, and/or your setting defined and is only really useful at night hence the name.
True Tone uses hardware (additional sensors) built into the iPad to automatically adjust the backlight based on the current lighting conditions. Thus making it impossible to incorporate true tone via software only.