Serde is very strong indeed (although not the easiest to understand, this would have been useful when I implemented a Serde library for [de]serialising with the AWS DynamoDB AttributeValue format).

That said, I've always had a slight problem with this approach to serialisation in general, which is that it makes it very hard to have multiple serialisation approaches for a single type (e.g. I want one casing rule for one target, and a different one for another). This seems effectively impossible with an approach based on annotations/macros. Would love to know how others have dealt with that.