I would think that there would be little to no chance of approval ever being granted due to the practical aspects of such an operation.
Any area of the Thames which may be commercially viable from a passenger viewpoint will almost certainly already be full of shipping of various kinds, there are very few - if any - areas within this area which could be developed for seaplane activity and the area is already a very busy one with regard to aviation.
That aside, the proposed destinations are unique but not exactly what you would have imagined being commercially viable.
I think someone has been on the Ouzo.