I want to migrate to an actual nested data-structure using (maybe) JSON - and these engineers absolutely will not write code, so config-as-code is a no-go, in addition to the disadvantage you mentioned.
My next thought was that there should be a better way to show the configuration, and allow that configuration to be modified. I was thinking maybe some sort of visual UI which where the user can navigate a representation of the final product, select a part and modify a parameter that way.
Is that along the lines of your suggestion? If not will you please expand a little? Configuration is the absolute core of this application.