See the merge request here, give it a thumbs up if you want to see this implemented.
I don’t have any issue with this being implemented, choice is good. On a personal level, I don’t know that I’d ever use it. I’m not sure why I would even want to flip the layout order. I just choose what I want seen all the time and leave it be.
Totally valid workflow! Not every feature is going to serve everyone, but this allows me (and others) to have one tray for system controls and one for background apps, on opposite ends of the panel. 
Or to just have your tray on the left side without it feeling awkward, for that matter. 