"Not too many objectors in the estuary"...seriously?! Apart from the entire environmental brigade, not just in this country but from across Europe, just for starters.
As for infrastructure, of course there will be upgrades, but that is exactly that; upgrades i.e. improvements to existing infrastructure. There is absolutely nothing in the estuary (apart from a load of birds) and hence there would have to be an entirely new infrastructure built to support the airport alone, costing many times more than mere upgrades to the existing stuff.
As for public enquiries, there will be enquiry after enquiry for whichever is proposed, and probably ones for solution that have been excluded as well, so I hardly think that this proposal is alone in that fact!
I'm well aware that this is just my opinion, and as many people will disagree as those who agree. However, I just can't see how east of London is the best solution even for London, let alone the rest of the country. Remember, this will be the UK's only hub airport, how is anyone from anywhere other than the south east going to be able to get there easily?!
In addition to this, it will be social and economic upheaval on a grand scale. The entire economy of west London will have to move to Kent; how fesible is that? Is Kent able to accomodate that? Will business even bother with the trouble, or just move elsewhere?
As I said, and as we all know, none of the solutions are perfect. But it seems to me that people are being very blinkered in that "it's either LHR or the estuary" when actually both of those still have massive issues that only look less bad when compared to each other, rather than looking at them rationally