I don't know if you are aware Rod but for non EU nationals who are permanent residents in an EU member state there is a path for them to transfer that residency to another state.
https://eur-lex.europa.eu/legal-content/EN/TXT/?uri=CELEX:32003L0109
Of course I don't know if you have permanent residence in France or if a person could take advantage of the option by dint of becoming a non EU citizen as a result of Brexit but I thought I'd just mention it anyway.
BTW I thought you were a bit harsh on Golandrina as living in Spain is something of a pre-requisite for a residency application so while maybe not a necessary question it was a valid one.