Also if you start trying to use DynamoDB like you would Mongo, you’re going to be really upset. The use cases, design considerations and performance considerations of DynamoDB compared to Mongo is night and day.
That being said, if I needed the flexibility and wanted to stay in the AWS ecosystem, I would use DocumentDB with Mongo compatibility. It uses the same storage engine as Aurora, it’s much more flexible and it doesn’t have any of the well known downsides of Mongo.
Hype and usage are very different. It's not like a lot of people really used it during the hype either. There are a few places which actually need something like that and can't use k8s.