[ Thanks to An Anonymous Reader for this link. ]
It looks like a new “locally integrated menu” will make
it into Unity, starting with version 5.6.0. There’s basically no
information about the new locally integrated menubar, except for
two bug reports which link to some custom Unity, Compiz, Metacity
and Light Themes branches so to see “LIM” in action, I’ve compiled
all these branches and here’s the result/