The no-short-flights-in-France policy has ended up utterly pointless and all about political greenwash.
It's only for cases where the train is under 2.5 hours. The French Govt wanted to give an exception where the flight is mainly connecting pax (e.g. for routes like Paris CDG to Lyon on Air France) but the EU decided this was anti-competitive and forced the French to drop the AirFrance-is-exempt clause. Routes from Lyon, Rennes and Nantes to CDG are not suspended because the EU considers the rail service not to be good enough. Thus the only routes which are now banned are from Paris ORY to Lyon, Rennes and Nantes - all routes which have already been closed. and I imagine the French Govt will ensure that SNCF doesn't make Lyon-CDG too good because it'll destroy a chunk of Air France's feed at CDG. The policy is only temporary and will be reviewed in 3 years time