Right now a master grid can be configured in code using the GridBuilder, but the detail grid needs to be configured  in a template and a whole lot of Javascript.
As it is much easier to prevent errors writing (and compiling) server side code using the GridBuilder than using large parts of Javascript.

In the good old MVC Extensions there was a method 

DetailView(detial => detail.ClientTemplate(MethodToCreateDetailGRidUsingGriudBuilder())

I would very much like the same approach in Kendo UI as it provides a more robuste method of building Detail Grids.