Love the enthusiasm Taller is Better, but don't think we will see a supertall building on that site. My hope is as follows:
1) Turn the old courthouse into a museum - a building as historic as it should be accessible to everyone. Plus, London has absolutely zero attractions and a city our size should have some kind of tourist attractions for it's own citizens and for tourists. We just had friends from England over to visit us and there was literally no where to take them. We took them downtown and they were bored silly.
2) Tear down the Middlesex County office building thing where the health unit is and either make it more parkland or possibly put a concert hall there. Or you could put an interesting lookout tower in that location. I've been to several cities in europe and a bell tower/lookout tower is very popular - one that you can walk stairs or a circular floor. Make it iconic looking and something that every person who visits London has to do. Really hope the city gets this land and does something great.