This is awfully negative. JSON explicitly does not declare the represented range of floats or integers, and doesn’t have a distinct arbitrary-precision decimal type. I haven’t read the Ion spec, only the description, but since it’s advertising arbitrary precision, presumably any implementation that does not support that is not a correct implementation at all.
In practice that means having (or adding) support for arbitrary numbers and decimals in the languages/platforms they want to cover. I am skeptic they would do that in C for example.
