I just tested on Mac and it seemed to work for me (I could get my steam user name, etc.). I used latest nwjs (46) and clicked on do not package.
app.nw is still created, but for me now, it's a directory (so I don't need to change the extension to zip, etc.)
So, just to make sure, here is the file directory I am adding the SDK libs and the new *.node files to:
Click on 'Show package contents' of nwjs application, then navigate to:
Add updated *.node, steam *.dylib files, steam_appid.txt here.