Would there be any particular security problem with user accounts being system users, where logged in users perform as their user and non-logged-in users have a

Would there be any particular security problem with user accounts being system users, where logged in users perform as their user and non-logged-in users have a guest account? Then make a noexec chroot which has just a /home for them all. I'm not sure how you'd translate a http request with an authenticated session into a handler running as a particular user, but I don't doubt that it is possible with some fork(), setuid() arrangement.