Chilli, London is no longer a Formula E city; the locals objected to the noise
and the disruption leading to the local government rescinding their consent to run the event, and somehow I think it's a strong likelihood that the NIMBYs will stop any future venue in the city.
Back to Silverstone. They already pack in as many spectators that they comfortably can, and at best they can only just manage to break even. That was 2015 (haven't seen the 2016 accounts yet) and in the previous years they made a loss on the race. What incentive could they possibly have had to deepen their losses even more by running a promotion in London that wouldn't earn them a penny more?