All good points, but one thing people should look at very closely before choosing DynamoDB as a primary db is the transaction limits. Most apps are going to have some operations that should be atomic and involve more than 25 items. With DynamoDB, your only option currently is to break these up into multiple transactions and hope none of them fail. But as you scale, eventually some will fail, while others in the same request succeed, leaving your data in an inconsistent state.

While this could be ok for some apps, I think for most use cases it's really bad and ends up being more trouble than what you save on ops in the long run, especially considering options like Aurora that, while not as hands-off as Dynamo, are still pretty low-maintenance and don't limit transactions at all.