If you are going to negotiate a deal, you are a fool if you do not carefully consider what the other side needs to get out of it. Me first negotiations take on the format of threats and work only if you have the power to threaten. So a look now at where the EU ought to be going might be useful.
There are a lot of problems in the EU. The Eurozone is not working fairly, neither can it with its present form of governance. The economic benefits of EU membership and being part of the Eurozone are uneven, favouring northern industrial countries led by Germany. Even in that group there is serious discontent with the economic outcome in France and Italy. All three have elections in 2017 which could throw up unwelcome surprises. The anti Brussels contagion has spread from the UK and the infection is growing. If the response is to loosen regulation and increase national sovereignty the euro will fail. If that happens the EU will unravel.
What has to happen in the EU is that all countries join the Euro, there is established an EU Federal government, elected by the EU parliament, because that is a properly elected body and should be invested with full federal powers. which then control a finance ministry and other ministries involving areas of policy now devolved to the Commission, which must be abolished. The Commissioners should disappear and the civil servants supporting them be dispersed into the ministries. EU wide taxes should be introduced and the current contribution system scrapped. The purpose is to inaugurate policies with a democratic mandate for the whole of the EU, especially for economics, which do not favour one country at the expense of another. The Council of Ministers could remain as a second chamber of government or Senate, with revising, but not executive, powers.
The effect would be a notable surrender of national sovereignty in exchange for a significant increase in democratic participation at federal level, which would usher in an era of improving prosperity and growth shared by all. In simple terms there would be a proper transfer of sovereignty from national governments to the people who would exercise it at two levels, national and federal. There should be no exceptions or opt outs. You are either in it hook line and sinker, or you are out of it entirely.
If all that happens (which it will eventually, but not in the Brexit timescale) the Brexit negotiations would be quite short and clear cut. GB would be out, but Scotland would have a greater incentive to stay within the UK, where its influence and independence would be greater than in a federal EU.