I think really the ideal would be to have a buttonless editor. I don't want to ever have to break in the middle of writing something in order to give it the styles that I want. The markdown shortcuts that have been added to the editor in recent versions of WordPress are a step in the right direction, and make many of these buttons entirely redundant. That doesn't meant that we should actually consider removing the buttons any time soon, because of the backward compatibility concerns for UX. But I'd much rather everything be done with keyboard shortcuts and markdown than having to jump around from the text to buttons all of the time.