I believe the FDA will likely grant AA to SRPT, because the drug has been proven safe and effective and there are no other treatment options. They will most likely also impose REMS on it, as EU should based on how small the trials have been.
This is then the best of all worlds. It gives patients treatment options while controlling risk.
Given the very small expected patient population, the risk is very small, thou the FDA is risk averse, which is why I think they will go AA with REMS.
75% chance it goes this way. 20% chance it doesn't get AA and has to do more trials, 5% chance it gets AA without any REMS.