How does that matter? We can create as many locales as we wish, some
with strict settings, others with settings selected from community
voted values; letting the user select at install time which locales
they wish to use.
The notion that we must have one and only one es_MX seems like an
auto-proposition. If we need to have only one es_MX because of
standards constraints then we can provide some GNU knob that says how
conforming you want the locale to behave and have the implementation
select a different file based on that.
Does that make sense?