I don't use connman, but I was intrigued by this bug, so I replaced ifupdown in a VM with connman.
1) connman is taking over the resolv.conf symlink because it provides an inbuilt dns caching server and assumes that the user wants to use it by default. 2) The package could ship "/etc/default/connman" with "CONNMAN_RUNSTATEDIR_RESOLVCONF=no" to reverse the current sysvrc default. It would then diverge from the systemd default, whose service unit doesn't source "/etc/default/connman" and sets up the resolv.conf symlink via "[/usr]/lib/tmpfiles.d/connman_resolvconf.conf".
