One thing about DRD on the whole is that it isn't something you can just copy and make work with a few days of CFD work. The way the switching works with the pressure differentials etc, it is very hard to figure out. So if lotus/mercedes/sauber can get theirs to work then they will have an advantage that other teams will have to work hard to make up.
One more problem about the DRD systems is that they have to be tuned for different air pressures. Not to mention if it rains that screws with the system horribly