Turns out there is another brilliant engineering design decision that's forcing further postponement. The Launch Termination System electrical system is completely independent of the rest of the launch systems electronics (for good reason). As a result, it's battery powered.
So far, so good. Rational system design.
Not so rational - the battery is life limited, with a maximum of 25 days from installation to when it needs to be serviced (just increased from 20 days in the last couple weeks) -
and it's not serviceable on the pad 
. So once the launch system leaves the Vehicle Assembly Building, they only have 25 days to launch it, or it needs to be returned to the VAB. That is simply horrible engineering - the sort of thing a first year engineering student would know better. $4 Billion plus per launch, and they couldn't be bothered to provision the Launch Termination System to be serviceable on the pad
.