Part of the original deal was that Emma would have to work or Shaw, and for that she would have two seats on the council. Emma negotiated to have 3 seats on the council. I'm pretty sure Shaw was the second seat, and Kitty would be the third. Even then, what is the advantage of just picking someone on the council? It's not voted, Xavier and Magneto picked everyone, wouldn't they have 12 seats on the council then?