Which parts of Brexit does this idea solve?
There is little or no common ground between Leave and Remain so I propose that the UK leave without a deal on the 29th March. Following that, set up a registration website for UK citizens to apply for EU citizenship. (Estonia already grants digital e-residency) Once granted, They go through the normal process of applying/renewing their EU passport and become official EU citizens. They will be granted residence and therefore they can get the full benefit being an EU Citizen. However, they will be liable for all financial, taxation, legal obligations and responsibilities shared by EU citizens. They will no longer be Defacto British citizens and will be regarded as a friendly alien resident. They will give up their rights as a UK citizen (voting etc.).