Your merged-ios-macos UI design is not radical enough. I do not have any design background, but I work in a public-listed company and I have been working on various C-level / board level presentation deck. IMO, the merged UI design will look more like iOS than macOS. If I have to design this new UI, I will not even bother with menu bar on top of the screen. Instead, I will make use of context-based slide bar from the left screen or right screen. Depending on the active app, the slide bar will show a different menu with large icons.
In addition, there are new human device interfaces (HDI) that need to be invented to make sure that a tablet can be an effective working device. Right now, even if there are voice-based control like Amazon Echo, it will still be very difficult to work, e.g. how can you prepare a contractual agreement using voice-based control? Very hard, especially if you need to work on a working document with trackable changes. How can you work on a spreadsheet to create financial model using voice-based control? Nearly impossible.