To be clear, I'm not saying it has to be literally Paxos as a service. There's a bunch of ways you can take operations from different sources in a distributed system and produce a consensus view of what happened first. But aside from trivial and low-performance options (e.g. everyone contends on a single DynamoDB item and uses conditional writes) Amazon hasn't made any of the possibilities available.

Isn't etcd or Zookeeper essentially Paxos as a service? Or maybe I'm missing exactly what's meant by this.

etcd is raft, but zookeeper is paxos as a service. so maybe a hosted version since zookeeper can be troublesome for folks to operate.