According to a long article in today's The Local, British subjects living in France WILL need a Carte de Sejour after Brexit. The folks who took the trouble to go to the British Embassy in Paris were assured of this, and were told to not procrastinate, but do it now!
Although we personally were told in May this year that it was not really worthwhile to have one, that was then and this is now. We can only assume that the report is accurate.
More doom and gloom! More advice on The Local French version.
Hang in there folks!!!