There is nothing in the estuary which is both a positive and negative, of course there will have to be links to existing infrastructure and in some cases completely new infrastructure created.
I don't see this as being either Heathrow or an other, I see this as trying to put together an integrated air travel infrastructure for the whole of Southern England, the point about the infrastructure already in place to serve Heathrow is valid and it makes no sense to relocate Heathrow.
Heathrow has finite capacity which needs to be addressed, Golf-Sierra makes a very good point about transit passengers, however they also have to share the connecting flights which means there will be an issue of cross London commuting which will need to be fast and efficient.
No chance of Manston expanding?