A bit of political reality:
(1) Boris is up for re-election and it's likely to be close. He may think (or be advised) that this idea will shore up the West Middlesex/North Surrey vote, but for every one who supports the idea, there will be those who have concerns about job losses.
There will be a question mark over the future economy of the above-mentioned area (and the rest of the Thames Valley as well) should the aviation and ancilliary industries up and leave. The amount of jobs generated by the aviation industry and large amount of companies that locate near Heathrow should not be underestimated.
(2) A consultation in March, an election in May - excellent timing. The first kicks it into the "long grass" long enough to be quietly ditched after the second. Boris can say that he has influence over the government and that Ken clearly would not.
(3) The government realises that its "no new runways in the south east" policy is unsustainable and may be softening the public up for the desperately needed U-turn.
It works like this:
(a) the consultation spells out the obvious;
(b) the government welcomes its conclusions;
(c) the government accepts that its "no new runways in the south east" policy is unsustainable and is holding the country back;
(d) the government caves in to the inevitable and "reluctantly" accepts that Heathrow expansion is the only viable alternative;
(e) Transport Secretary Justine Greening gets promoted out of the way.
(4) Labour has seen this coming and so is now against Heathrow expansion in order to oppose the government for the sake of it.
The government often repeats the mantra of "better airports not bigger airports". In the case of Heathrow, bigger IS better, because it is the only workable way to deal with an airport that has been allowed to operate at virtually 100% capacity.
Are we talking about a "new hub airport for the south east" or specifically about an estauary airport? If it's the latter, is it the artificial island south east of Southend, or the reclaimed land north east of Chatham? If we are talking about the former, then the only sustainable location is immediately north of Heathrow, between the A4 and the M4.
Finally, will this white elephant be built before the other one (HS2)?