In principle, seems like it should work to allow large scale distribution across many servers. But the actual management of replicas and deciding which servers to place partitions, redistributing when new servers are added, etc. could lead to a massive amount of operational overhead.
Main downside is that you either have to either self-manage the deployment in AWS EC2 or use Azure's AWS-RDS-equivalent (CitusData was acquired by MS years ago).
FWIW, I've heard that people using Azure's solution are pretty satisfied with it, but if you're 100% on AWS going outside that fold at all might be a con for you.
If you are interested in partitioning in an OLAP scenario, this will soon be coming to pg_analytics, and some other Postgres OLAP providers like Timescale offer it already