Our use case is that we leverage derived models to serve as DTO's in our application APIs, and when we add a column on a table we (99% of the time) want that to show up on the DTO.
It doesn't happen often enough to warrant us devoting dev resources to figure out how to write a plugin, but it does happen often enough that it becomes a pain point when we make a schema change, refresh, and then either forget to go find all of the places we reference that entity in our model and add it, or remember, but miss one or two places.
Having a setting on either the model or on the derived element that told LLBLGen Pro to sync fiend changes on entities to their respective elements, or even having a task that you could run (similar to sync relational data) would be a very useful feature.