Would be curious to know is PRAM zapping followed by a simple chflags from the startup disk would permanently change the visibility of Users and Shared. I didn't think of trying this before applying the given fix, and now I've run out test machines...
I'm curious about this too although chflags won't solve the permissions issue. I have a couple machines I can test at home tonight.
This fix did resolve it on a 2012 MBP and Air.