I think shabbar is getting promoted to advisor so he can attend cabinet meetings. Shabbar zaidi is basically a policy guy and not a manager. He can give great ideas to collect tax and block tax leakages but I doubt he can manage the corrupt FBR machinery. FBR has 20,000 employees and needs a powerful administrator.
My suggestion would be to make some army guy chairman FBR. This will also send a message to all tax evaders and non filers.