Although I don't agree at all, I don't think that the teams would be too upset by it. If I were team manager at one of the topteams, I'd reduce my team to 2 cars and if the third driver can find enough sponsoring budget to run 2 others cars, together with the fourth driver that is, I'd support them as well. Which means 2 teams but 4 cars.
El Matador brought in enough money to support a third car at Citroën. Afterall they intended to enter only 2 - Seb and Colin, but with Movistar money, Carlos got a complete season as well.
But still this new rule shows how incompetent the guys at FIA are with their over-regulating rulings.