We have a deadline
Thanks Boris, and thanks to the 13,966,565 Britons who voted to make him Prime Minister. Up til now our plan to escape to France has been somewhat open ended, predicated as it was on my wife being a UK citizen who could move freely within the European Union. Over the last three years of high Brexit drama we've watched as plans were drafted, then abandoned, then drafted again, and as one deadline after another came and went.
I still feel sorry for Theresa May.
Now Boris has the power to force through his Brexit "deal." That isn't actually even remotely close to a real agreement in how to disentangle then restore a working relationship with the EU; it's just the first step when the UK government says "OK, we're out of here!"
Following that is what will likely be years of negotiations with the EU, and with all of the trading partners who up til now were included in EU trade deals. All of that has been thrown out the window and everything is up for grabs. If recent history is any indication I'd expect that the US will rape and pillage the UK economy, after which other countries will pick from the scraps left behind.
It's a good time to not be living in the UK.
Our move to France now has a somewhat fixed deadline: December 31, 2020. In the current withdrawal agreement that Boris is about to present to his Parliament that is the end of the "transition period." In theory at the end of those twelve months all UK/EU negotiations will have been completed, and Brexit will be a done deal. I'm highly sceptical, but for now that's the point when we move from being "EU resident moving from Britain to France" to "Foreigner moving to France."
If you are ‘legally resident’ on transition day (31 December 2020) you can stay. This is known as the 'effective date'. This includes people who have moved to the EU27 up to the end of transition on 31 December 2020, who will be covered by the Withdrawal Agreement on the same terms as those present before Brexit day itself. The current conditions for legal residence under EU law will apply. After 3 months you have to be working/self-employed, self-sufficient, a student or a family member of any such person.
In practical terms the goal is now to purchase property in France by next summer, and be living there by the fall. Now the real work begins.