To traverse a dataset from its last record to its first, let the user provide a dataset option ReversedOrder="Y"|"YES".
Let this work with SET, MERGE, UPDATE statements, and for any procedures that read datasets, applying only when the dataset is being read.
I have no idea how feasible this is, but I've frequently encountered situations where I would want to do this. It feels mathematically unnecessary to have to resort a dataset in descending order just to -- or to sort datasets in descending order, and provide an index in ascending order just to -- have this capability.
I would love to know why this couldn't be done, but not as much as having the ability to do it.