Reasoning:
a) The Ubuntu button as well as the launcher make more sense on the right, where all the other system-related buttons are. It would help maintain users' focus on the current application if all the file-related commands were on the left and all the system-related ones on the right.
b) If the Ubuntu button were to be moved right, window buttons could be slightly shifted to the left corner. That means that there would be two very useful corners, quickly reachable by mouse (as per Fitts's law) -- the left one for closing an application, the right one for all the things the Ubuntu button will do.
c) As the Ubuntu button can act as a "hot corner", it makes sense to put it on the right, away from application-related buttons. That way, when you're working with an app, you won't accidentally trigger the launcher.
d) If applications have vertical toolbars/sidebars, they're often on the left (e. g. most image editing apps have "Tools" on the left, most file browsers have a left sidebar, etc.), so they are, of course, easier to target when there's no launcher on the left.
Would it be possible to add this option?