It's elegant, but will it be enough? What happens if the pebbled service is (mysteriously) started when rockpool is already running? Who "wins"? What happens if a user installs pebble after installing rockpool?

From systemd's manpage: "If a unit has a Conflicts= setting on another unit, starting the former will stop the latter and vice versa". This sounds much like the current situation: either pebbled is running, or rockpool, but you don't know which one.

I don't know if this kind of conflict resolution can be resolved using a systemd unit configuration.