I agree. This is now a mandatory rule by the government of India.
I doubt if this can be implemented in the core nopCommerce as it would be targetting only country-specific stores. Rather an ideal choice would be through a plugin.
I would happily spend time with the developers who would like to develop the GST plugin for India. And Buy it GLADLY. I'm sure every single store owner from India would immediately buy this plugin installed.
Reach me if anyone wants to work on this plugin project.