Also, wouldn't it be possible that every account holder had the option in his own account to either select a 4 or 13 week power down?
Absolutely. And keep in mind that 4 weeks and 13 weeks are random numbers. They have no meaning and the powerdown period in the future should be far more dynamic than that.
ideally I would like the option to extend PD for certain long term savings accounts and have others in 4 weeks etc, but I don't see that being possible for this HF due to complexity, 4 week only is a simple number change.