We have encountered a use case in our system where we have a few fields (Severity. Risk etc) with a closed set of values, where the sort order for these values is pre-determined but not lexicographic (Critical is higher than High). Generically this is very close to how enums work.
To implement, I have prototyped a new type of field: EnumField where the inputs are a closed predefined set of strings in a special configuration file (similar to currency.xml).
The code is based on 4.2.1.