1) As a reader I don't read that much to justify a separate ebook device. I am cautiously optimistic about iPad Pro for documents / articles / papers etc. Also highlighting with pencil.
2) Split Keyboard. Air will force me to use regular keyboard, and I will get RSI after long typing sessions. I think iPad Pro + Dock + small ergo keyboard will be about the same weight as Air.
3) Sketching, drawing, highlighting (via Pencil). Seems nice to have the alternative way of input/draw things / diagram stuff. Also promising for PDF annotation etc.
4) Form factor, seems like it's easier to take iPad Pro to the park to read/ browse / check emails. Not entirely sure about this point though.
Thanks for explaining. I come down on the other side of all your points, but I can see why you would consider an iPad over an Air.
It's a shame you can't develop on the iPad or run a web browser that is not Safari or Safari with a wig.