I'm actually saying we already have a system for binding a POJO (plain-old Java object) to UI fields, including annotations for things like ranges and allowed values.

How I would envision this working, as a modder, is I'ld create a pojo class (probably a component) and just say this is the configuration class for my generator. The fields of the class may need to be annotated (ask @synopia about the annotations he made for the behavior nodes), but you can discover what fields are available and access them through the class and field metadata system.

This is perhaps an idealized goal, but it simplifies things for generator developers. Particularly if the configuration is going to be saved as a component on the world entity - you have the component anyway, might as well make full use of it. Or is this asking too much from a first cut?