Re Gibraltar - the counter is Ceuta.
If Britain's claim to Gibraltar is invalid. Spain's claim to Ceuta across the water is equally so. Go back to the days of the Tangiers Regiment and swap?
Re Who is next?
I put my money on the Dutch and the Danes. Although Hollande and Merkel both have to get through elections in 2017. And the Brits will still be negotiating then.
Re Britain's position.
The Poles, Estonians, Latvians, Lithuanians, Swedes, Finns, Danes, Poles, Romanians, Hungarians, Czechs and Slovaks all want something that Britain can offer - Britain's forces and its nuclear umbrella. They also want access to Britain and the world's 5th largest economy. The same goes for Cyprus and Malta.
The core anti-Brit vote will come from those currently in power in Brussels, Luxembourg and Paris. As usual.
Everything takes time and nothing is ever what it seems. Politicians and bureaucrats will continue to play the same game with modified rules.
Scotland is not a country, no more than Northern Ireland and certainly not London. Sturgeon is reduced to hoping that Sadiq Khan, the Lord Mayor of London will assist her in getting a seat at the negotiating table. Spain, France and every other country with a separatist tendency will reject that. Scotland has to become a country before it can apply to become an EU member.