I generally avoid installing software from AUR to prevent any possible issues with packages I could have, however I have a crap ton of XFCE plugins that I think could be included in the repositories. These include:
Very useful for switching panel layouts and probably the most necessary package in my list. I would go as far to say that this package should be installed by default in the XFCE edition of Manjaro.
Not all users are going to want this, but I personally love having a places menu in XFCE like in Budgie.
Without this plugin, there is no way to have a Windows 7 taskbar in XFCE.
I guess not many people would want this since you would most likely just use GNOME if you wanted this kind of workflow, but I still think users should have the option to install it.
Without these packages (assuming you don't know about or don't want to use the AUR) you might come to the conclusion that XFCE isn't very configurable even though it's way more free than Mate or Cinnamon while not having the excess of KDE.