1) The following is completely false:
Updating to 0.16.3 from 0.16.0-2 for a non sophisticated Linux user may be prohibitively complex.
This assumes that: a) Everyone uses Linux. b) That people using Linux don't have an easy method for updating. This is false; most non-sophisticated (if not ALL such users) are going to be using something like Ubuntu or Mint which has PPA and updating is trivial.
Updating Windows and Mac is very trivial. If you know how to install Bitcoin Core, then you should know how to update it.
Anyone have any thoughts or info on how much of a focus streamlining updates across different OS's and Linux Dsitributions currently is?
2) Updates can never be automatic for a decentralized system as such. Even adding something like a 'update available' notification system can open up more attack vectors and is (as always) prone to abuse.