[tjonker]

Ion's equivalently-expressive text and binary formats is absolutely central to its design, and IMO one of its most compelling features. You don't have to choose between "human readable" or "compact and fast", you can switch between them at will. This helps Ion meet the requirements of a broader set of applications, eliminating the cost and complexity and impedance-mismatch problems you get by transforming between multiple serialization formats.

[viraptor]

I get that binary format is nice, but I just don't get why instead of adding binary format to an existing good text format Amazon decided to first extend a poor text format and then add binary to that.

Basically: Ion == JSON + extra features + binary format spec. But Ion ~= YAML + binary format spec. You're going to write a new serializer/deserializer in both cases anyway, but in the second one, at least you get the text part for free in almost any language available.