Idea: All of the countries, realms, territories, Crown Dependencies, British Overseas Territories, Sovereign Base Areas, patches of nowhere, etc. of which HM Elizabeth II is Queen should unify as a single country. Members of the current British Commonwealth that do not have the Queen (e.g. India) and/or countries that were formerly British territories or colonies and that are not currently Commonwealth members (e.g. Republic of Ireland, USA) could be given the option of joining, but probably will choose not to.
There would be a currency union, so there would no longer be Australian Dollars, Canadian Dollars, etc., but a single currency, which could be the current Pound Sterling but could be a brand new currency or maybe even the Euro.
National divisions (e.g. Canadian provinces and territories, Australian states and territories, constituent countries of the UK, etc.) could retain some sort of Federal or devolved jurisdiction if the people wanted to, and entire former countries, dependencies, etc. could form a single sub-national jurisdiction if they wanted to, e.g. a “Province of Jamaica”.
Citizenship laws would be unified to create a single national citizenship. Anyone holding citizenship in any of the unifying jurisdictions would automatically become a citizen of the new unified country. No-one would become a foreigner in their homeland unless they specifically applied to renounce the new citizenship. Migration laws would be unified into a single immigration zone and it would be as easy to move from New South Wales to Jersey as it currently is for a US Citizen to move from California to New Jersey. Immigrants from outside the unifying countries that have already fulfilled the requirements to immigrate to one of the unifying countries (e.g. Landed Immigrant status in Canada, Leave to Remain in the UK, settlement in the UK on the basis of Irish Citizenship) would be grandfathered in and granted immigrant status in the new country. New immigrants would have to fulfill the immigration requirements of the unified country.
Good idea? Bad idea? What kind of economic, cultural, political, or diplomatic effects do you think this would have? Would the movement for Quebec independence finally reach critical mass?