ENCODING I/O specifier

Dear all,

I'm looking at the Fortran 2003 standard description of the ENCODING
specifier, and I'm amazed that the standard actually restrict this to
only have the values DEFAULT or UTF-8. What could be the rationale for
not allowing, for example, a compiler to implement other Unicode
encoding. I understand the need to not require too much from the
compiler, but why restrict what can be done?

Thanks for your insight in this.

-- 
FX