A court in Germany just ended the last lawsuite against the new Berlin-Brandenburg-International Airport. It looks like finally the work can begin.
As much Tempelhof has historic value it is not really any longer pratical for commercial air traffic. I hope that they will keep the building and maybe use it as a museum or something. It would be really a shame if this historic monument on would be destroyed.
Tegel on the other hand could maybe used a similiar way like London City Airport but somehow I doubt that the demand of business travel in Berlin justifies two commerical airports. Berlin is not London.