What is the true limit? Why not the Air 4? RAM constraints? It’s difficult to explain this at this point. The Standard A12 cannot run it? How much RAM is really needed? Is 4GB not enough? 1st gen 12.9-inch iPad Pro? 2nd gen iPad Pros? What’s the real technical cutoff?
I reckon that the only iPad Pro that might be truly, technically inadequate to run it is the 9.7-inch iPad Pro, 2GB of RAM might actually be too little. As for the rest? Pro and non-Pros, I’m not sure. After Apple faltered on their explanation, I don’t think we can identify the true lower bound specs required.