Let me explain to you Mr AC that a standard STANDARDIZE the way to do things.
Being able to specif things in a standard way allows automatic compatibility from everything that implements the standard with anything else that implements it.
Standardizing the way of making user-defined literals is not the same as having a standard way of having a particular kind of literal.
Try to think about this: 'Everything you didn't specify will fall/fail/won't work at some point'.
It's already being done with other programming languages. (Java 7 comes to mind)
It doesn't require a large addition of the standard and can make life easier for people making software.