If the performance isn't interesting it may still be worth adding for
compliance reasons, but if we can only add IEEE-compliant decimal FP by using non-SQL-standard type names I don't think that's super useful. If there are significant performance/space gains to be had, we could consider introducing DECIMAL32/64/128 types with the same names used by DB2, so people could explicitly choose to use them where appropriate.
+1 for using the DB2 names.
On reflection, I should offer more than +1. I think that the IBM name DECFLOAT(16) is better than DECIMAL64 because:
1) The number of significant decimal digits is probably of greater importance to a typical end user than the number of binary digits used to store it. 2) Other SQL types are parameterised with this notation, such as VARCHAR(6) and DECIMAL(6, 2). 3) IEEE 754 has rather different semantics to SQL DECIMAL, I'm thinking mainly of the behaviour of special values, so using a name like DECFLOAT(n) instead of DECIMAL64 would draw greater attention to that fact (ie it's not just a fixed sized DECIMAL).
Also, IBM was here first, and I *guess* they will propose DECFLOAT for standardisation (they are behind proposals to add support to many other languages), though I have no information on that.