> These configuration languages are just different syntaxes for expressing the same fundamental data, bearing the same semantics.

This is my complaint too. However, they do add a proper integer type, which is the only thing that they do change with the data, as far as I can tell.

> It would be much more interesting to see a language which experiments with what is fundamentally representable

DER (and TER, which is a text format I made up to be compiled into DER (although TER is not really intended to be used directly in application programs); so TER does have comments, hexadecimal numeric literals, and other syntax features) does support many more data types, such as arbitrarily long integers, ASCII, ISO 2022, etc. My own extension to the format adds some additional types, such as a key/value list type and a TRON string type; the key/value list type is the only nonstandard ASN.1 type needed (together with a few of the standard ASN.1 types: sequence, real, UTF-8 string, null, boolean) to represent the same data as JSON does.

> for example like how the Nix language supports functional programming and has functions as a first-class data type.

For some applications this is useful and good but in others it is undesirable, I think.