The lack of a timestap datatype is a problem, but the lack of a 'link' datatype is imo a greater one, now that people are doing supposedly-RESTful APIs with JSON payload. Which is not to say that you can't layer that type info on top of JSON (see e.g. HAL) but you do need both ends to agree that that's what you're doing otherwise it kind of treads on the "no out-of-band info" property