Thanks for the ideas - encrypted home dirs has been superseded by LUKS full-disk encryption so I wonder what use-case you have in mind for this that FDE does not already accomplish?
Guest sessions have been discussed a bit in the past - see Guest sessions in 18.04 LTS - are they needed? and Brain dump on guest session progress for the history - I believe the progress for this is being tracked on launchpad if you want to follow along.