Quote - Also, limiting the shading tools to read-only is really, really limiting

That needs a little qualification. Although a materials or shader (mc6 and mt5 equivalents, respectively) preset saved from surfaces created in Shader Mixer do not allow the brick layout to be edited in DS 3 base and so the basic function is fixed, the parameters are accessible in the Surfaces palette so there is still scope for adjustment, depending on what options the maker has left exposed and how clearly they are labelled and explained. Shader Builder is a GUI for building regular RSL shaders and their DS support scripts, so those will again work like any other shader with parameters in the Surfaces palette that will allow as much configuration as the author was willing and able to provide.