1. Magny Cours was trash. It was already born too short and tight and nothing ever made it better;
2. Eliminating the Mistral chincane entirely is a simple and very good fix. It would naturally mandate low downforce settings, which are very rarely put in action, and have teams and drivers tackling less familiar settings. Variety, it's good for racing. The full Mistral straight would be long enough to perhaps negate the need for DRS. This in would result in teams and drivers having to decide whether they'd make up their time down the straights or in the corners. Making a wrong choice would be much more costly because drivers would be much more vunerable in one sector, or another.
3. Other than that, another good option would be to alter turns 1 and 2 so drivers would go flat out all the way between what is now turns 15 and 3. It would, to a lesser degree, mimic the effect of eliminating the chincane down Mistral, which I prefer. There is already a built in layout option for this.
4. Reverting to the the short 1990 layout would not be a poor decision as well. Such a short and quick lap would create a unique scenario of leading drivers facing much more chaos through traffic and possibly smaller windows for under and over cuts. It would make Paul Ricard something like F1's Norisring with drivers just banging quick laps one after another and with no shortage of action for the spectators.
5. Another idea would be to bypass turn 14. Have drivers go from turn 13 exit through a 'bent' straight connecting the circuit to the main straight. The main straight would have much more action and the circuit would ignore two corners which do not work so well for F1.