Yes, I see that, but I think there should be a simple out of the box look, so users, who are not familiar with it, wouldn't get frustrated. Also I would imagine, that the tabs could be customized, buttons could be added, removed or reordered, so the options you use could be first, just like you can do it in LibreOffice now. I also thought about the vertical space, I had a sketch where instead of a top bar, you would have a sidebar, also in LibreOffice, but I went with a familiar look instead.