Totally a political promise made by the kind of people who think subway tickets cost 5€ and only use official cars that comes with driver and parking.
I hate cars in Paris as much as anyone, but they are required in a number of cases and this measure will hugely impact negatively the mid-class and poors that needs to commute to Paris for work, while not impacting the (very) richs that can live in the center.
It's also critical to have a strong urban planning policy that allows people to live near to where jobs and transport hubs are. Suburbs inherently advantage car owners (and, consequently, the richer people that can afford to own a car).
[1] See, for example, data from the UK: https://www.ons.gov.uk/peoplepopulationandcommunity/personal...
Also subway cost 35€ a month (well, 70 if you're not working), or ~20 a week if you're a tourist (unless you take one-use ticket, but don't do that, especially if you arrive by the airport). One-use ticket if you stay within Paris last 2 hours and cost ~2€, but it is more expensive if you're not actually in Paris (i think its 15€ from CDG to the center).