Hello, thank you for getting in touch and for your support!
Extending Multi-Pass to Surface Shaders is actually something we plan to do in the future, as soon as we feel that the template system is robust enough. Although there is no official date for this, I'll be registering your interest so that we can get back to you on this.
Shader templates are quite advanced and flexible, but they do require some shader knowledge in order to set up. We do provide a basic
multi-pass example in our wiki, where we also focus on explaining its specific tags and behaviors.
Please let me know if you have any further questions, thanks!