check back in Dec 2016 to see if I am right
You get what you pay for :-) But I think all you need is something like Lightroom Mobile but programmed from an iPad Pro point of view first (i.e. including stylus and keyboard and solving the external storage / SD import problem AND not needing desktop sync or any other legacy kludges)!!!!!!
Don't buy the companies Google. Instead fly them to Mountain View for 1-4 months and fund them to get their Android-only RAW camera (only Android has RAW APIs; iOS doesn't; Windows Phone does but nobody it breaks my heart to say it cares about Nokia er Microsoft phones and Windows Phone) apps as awesome as possible on Nexus 6, Nexus 5 . . .