Having read the articles on https://www.service-public.fr/particuliers/vosdroits/F12017, I can't see any advantage for myself and spouse as we have been resident for 10 years. After 5 years' residence our right to reside is permanent, as I understand it. If the UK ceases to be in the UE, I don't believe our residency will change, although I could understand if the French insisted that we maintained a guaranteed bank balance in France or otherwise illustrated our capability to continue our retirement in France without cost to the state. Our medical costs can still be cross-charged to the UK, we don't ask France for a pension or financial support, and we pay income and local taxes to France, and have no French debts.
For people running businesses in France or employed here, the Carte may be advantageous, but I couldn't say.