Update from last November, just in case of use to others going though the process.
I had my interview today, 16months after submitting my huge dossier. I was given only 12 days notice and was also required to bring another huge dossier as all the documents that were now out of date had to be resubmitted, and in some cases re-translated. Applying for naturalisation can be costly.
So have been buried in revision for last 12 days. This was a useful link:
It was a very friendly interview, in three parts. The first was going through my dossier - particularly the financial element as she wanted to be clear exactly what was my income. The funniest thing was I had been asked to bring in justificatifs of income over last 3 months, so brought bank statements as don’t have pay slips. She handed these back as being “personal information”! They know everything else about me!,
The second, longest, section was on how I have ended up in France and in this area and how I have integrated into my local community. It felt very relaxed as if she wasn’t looking to trip me up but just wanted me to explain my relationship with France over my life and why I wanted to be French. We talked about my family history, my time in France as a child, why my husband hasn’t applied, and what prompted me to apply (not just Brexit although she did ask). Also who my friends are, what I do with them, the role I play in my commune, the various associations I belong to, where I go on holiday, We talked about our gîte, and the clients, and about the area we live in.
At one point I mis-pronounced a word, which she corrected. I apologised but she reassured me and said my french was fine, but I still had an accent 
. (1) As I said, a nice woman… I also managed to say the devise of France was liberté, égalité and fidélité. Her “really?” Allowed me to correct myself.
The third section was THE questions…devise and what each mean, the symbols of France (with her turning her head to stare at the bust of Marianne on a shelf (nice woman) …and we had a discussion about the new Marianne engagé), the revolution why and who, the Veme republic and the changes in powers, a bit about Algeria, etc etc. All very much as the in the video link. The one question I didn’t expect was to name the current political parties…
And then the final killer question of whether I felt French! Which is impossible to answer as I’m not French so I have no idea what “feeling French” is like. So had to fluff around and said I didn’t feel english.
But generally I left feeling that I had been able to explain myself and demonstrate a certain amount of knowledge. Hopefully enough but will be 18months before I know.
(1) edit…my French is not fine, she was being polite! It is above B1, the level required, but not completely fluent by any means.