Hey Forum,
This is my usecase, I want to dynamically create a json and feed it to system.tag.configure(..) afterward.
For example, I need to have a UI that will step one, get the tag type (memory, opc ..) that the user need to add. After that dynamically with the help of ignition, I need to get all "Possible" inputs for a specific tag type in order to propose that to the user.
Is this feasible? 
It doesn't take json. It takes lists of dictionaries, with possible nested dictionaries.
Yes, using ConfigurationPropertyModel.getApplicableProperties(), after retrieving the tag provider's model from the tag provider, which you would get from the gateway context. (The easiest way to get that latter is via system.util.toolkitCtx() in my Integration Toolkit.)
There's some sample code in the providers script in my Tag Report Utility exchange project that you might find helpful.