I just received my iPad Pro (for work) and I will also be going into this experiment. I believe I may have a different experience since I have used a regular sized iPad for 3 years already with success, even though it took me a while to get it optimized for my work flow. I totally agree with your assessment of a lack of a file system. That has always been my gripe with ios. I’ve been using Google docs as my personal file system and Ive been able to connect to works servers via Good Reader so while it’s a bit cumbersome like everything else in life once you get used to it things work.
I’m mostly excited about the apple pencil and how it can and should enhance my ability to markup creative documents. We’ll see.