Airport in the sea, terminals "...over a rail line (that is not a spur or branch line)...". Do you mean the west coast main line near Warringtion or Preston?
How can there be "...no on-site parking...", where do you park if arriving by road (e.g. shift staff travelling when the trains are not running, or there's engineering work)?
"...Ditch the shopping complex and have the transfer lounges remotely located as well..." how then can the airport operator make money?
What happens to Blackpool and Liverpool airports?
Lovely bit of fantasy, but it's hardly a good business proposition, so who do you imagine would pay for this nonsense?
Which carriers do you imagine would be prepared to use this "white elephant" airport?
Let's face it, carriers won't shift to the estuary (should it ever be built), hence Boris wants Heathrow closed, do you really think they'll go to Liverpool or Blackpool?
Do you really think that Heathrow's owners would be pouring in money to rebuild terminals if the airport was likely to close in the next 30 years?