I only have the 12.9 pro. But I would love refinements on the pencil. I find it very slick on the screen. More textured feel like a cintiq would be great. Also, I find the palm rejection to be subpar. I get lots of marks and gesture inputs that I don't want happening .
Tilt is ok but could be better. Barrel Rotation would make the pencil a artists dream (like Wacom art pen)
More ram would be nice, I paint at super high resolutions and I get limited to only a few layers at times.
A faster processor would always be nice.
But I would rather have More battery life please. I kill mine in 4-5 hours in bright environments.
The screen is great, just not in bright environments .
Better color management would be nice. My workstation has color calibrated cintiq 27. I notice when I import into the iPad the colors are off. I did find an app that can display color calibrated images, and ca,I rates with my color calibrator, but I can't find a way to calibrate the system, so everything I create in the iPad has to be adjusted in a color managed workspace later. Kinda a pain for printing and posting stuff on the web. Even if the new small iPad has more accurate colors, screens drift in a month. Colors get off in time, system wide calibration is a must for professionals.
Overall, I'm very happy with my iPad . I sold off my cintiq companion because I was hardly using it after the iPad purchase. If I don't see any improvements in these areas, I'll probably just keep the old one. It's fine for mobile sketching/painting, editing photos, and consumption
A really cool feature I would buy, is the ability to plug iPad into a computer and have full resolution cintiq like screen. That way we could have OS X on the iPad Pro. Astropad sucks for my needs. We need hardware screen capture like the cintiq companion does.