I think this would be an excellent idea. The usual answers is ‘fly on Expert’ but this is not always possible, especially if you want to fly with traffic …just avoid SoCal on TS1.
You can’t give controllers a test before they can control on TS1, that just isn’t possible or practical, but by limiting it to a certain grade would mean that the person in question has had some experience of being controlled before they are able to gain access and so will have experience of what is expected by a controller.
Other option would be to have a grading system like we used to have for pilots. When you first control you are limited to perhaps C and D air spaces, as you have more ‘operations’ you gain gain higher class airfields with eventually being able to control Apr and then Centre?
No if your usual reply when some says they have issues with ATC on TS1 please come up with a better answere then “Fly on Expert” as that does not add to the value of the conversation. It’s good to see IFVATC and IFTSATC trying to do something about this.