FWIW, the SLS gets around this by having explosive bolts in the hinges that blow when the car is past something like 90˚ in orientation and has a velocity of 0 for more than N seconds. However, the SLS is a $300k car, so no expense is spared. That solution might be a little less feasible for a car that costs what the Model X will.
I dunno, given the other story today[1] about the Tesla S blowing away everyone else in safety tests, I wouldn't put it past them to have considered escapability after a roll-over in the X.