Hi,
maybe I'm too picky, but I have couple of questions/remarks regarding current Nautilus UI.
Now, I'm happy that new features were added/reorganized, but it does feel it is a little bit chaotic right now.

I would expect the left/right history buttons being right next to the History Navigator selector. That way history-related controls are together and the purpose of the buttons is obvious
"Hier.", "Com."... abbreviating button labels? Really?
And finally, why was part of the buttons moved up? And part stayed down?
I know that you wanted to distinguish "Scoped", because it opens a new browser, and Variables, because they have intermediate menu (and later open another menu).
But I think the fact that Variables are tied to a particular selected class would make much more sense to place the button beside hierachy/class button.
Placing them all on a single line would also save up vertical space, which considering we've added QualityAssistant and Rubric adds another line is quite valuable.
(And finally the width of the buttons should perhaps match more closely the actual needs of the label, because now it's bit cramped.)

And finally, code-wise I've never really interacted with Morphic and stayed in Spec, so when I was digging through code it seems that the way Morphs are composed are through these "addMorph:fullFrame: (LayoutFrame identity rightFraction: 0.10; yourself);" constructs sprinkled haphazardly throughout the code. Is there nothing like SpecLayout? Maybe it wasn't so hard once you get used to Morphic, because I spent probably more time doing elementary changes to layout than learning half of Spec... (Also since Spec can interoperate with Morphic, maybe the layout could also be adapted? Or slowly migrate Nautilus to Spec (if there are even plans like that)?)
Now as I've mentioned I'm not an UI/UX expert, but you don't need to be a chef to tell when food isn't great (which is of course amplified by personal tastes).
So unless I am the only person bothered by this, I would like to raise a discussion (or send a slice, but the way I've done the layout weirds me out, so I still want to look into that regardless).
Cheers,
Peter