What's France Millionaire's tax ? I guess you mean the wealth tax, or Impot de solidarité sur la Fortune, it dates already several decades and is still alive and kicking, despite all arguments laid out in favour of removing it, the political price for anyone to cancel that tax seems too heavy in the local landscape (it was removed from 1986 to 1988 though according to the link below ) https://en.wikipedia.org/wiki/Solidarity_tax_on_wealth
No it is not that tax. It is a tax on all income above 1 million euro and taxation is 75%. And that tax does not exist for decades. Existed around 2 years. https://www.theguardian.com/world/2014/dec/31/france-drops-75percent-supertax
Indeed, that's another tax, you are right. When Hollande was elected, I was following rental ads in Paris for larger posh apartments and houses and the offer suddenly increased hugely, as of a couple of years ago luxury market especially in the areas favoured by wealthy locals was almost dead, although last I was there it seemed to have picked up quite a bit.