If the maths work out that having Ark-Royal as a tourist attraction all well and good, but otherwise why bother putting a boat there. There are plenty of chunks of land around that area that could be used as a "proper" heliport.
Personally I think that a proper heliport on the north of the river between docklands and westminster somewhere makes sense at a basic level but you need to get away from paying £1500 a day to land and sit there or a bit before it would become used as a taxi-rank, if that is what people want though?
On the other hand, as there is a great big airport not 500m away wouldn't it make a bit more sense to have a sensible place to have helis land there?
I understand the need for airliner safety/separation but I can't see how landing on the Ark Royal in the general vicinity would be much safer, particularly if operating under a different ATC unit.
CITY never seems that busy that it couldn't accommodate a few helis!
CC