The outcome of the negotiations really hinge on the relative strengths of politics over economics when it comes to the hard graft of haggling. The EU has been stressing politics over economics, that Britain's departure has weakened EU unity and she must be punished for it, she cannot be seen to benefit from Brexit and she will not.
We've been banging out the economic "why cut off your nose to spite your face" argument, so we've had the Governor of the Bank of England talking up the importance of the City and Hammond stressing the importance of the UK as a market for EU goods and threatening to turn us into a tax haven. Boris tried this in his early days as foreign secretary but stopped when he insulted every European he spoke to.
Pivotal to this is Germany, all the indications are she's full square behind the political argument, but if she could be persuaded by the economics we would get a much easier ride. Theresa May might, though these are early days, be trying to position herself as honest broker between Trump and Merkel. Trump, even by his own standards, seems overly keen to pick a fight with Germany for no apparent reason, conspirator theorist say it's all to do with Russia, but regardless, something is going on. If May could patch things up between the two of them, turn the gas down on it, or at the very least get Trump to stop threatening German car manufacturers, then Merkel might be a bit more persuadable over Brexit. It should be remembered that Obama bypassed the UK when dealing with Europe and was very pally with Merkel, that's not how the special relationship is supposed to work and it is one of the reasons Farage talks so scathingly about Obama. If the Anglo Saxon conspiracy (as the French call it) is going to be dusted off and back on the road and May plays her cards right we might come out of this Brexit bullshit with our trousers, if not our shirt.