Until we know the damage to the unit 4 SPF, we likely cannot offer anything specific at this point. We know there was likely boil-off of the coolant inventory, but again that relates to loss of onsite power. If there was damage to the SFP from the earthquake itself, then some strengthening is indicated. Some have suggested further redundancy in the cooling systems but in this case, without onsite AC, those won't do you any more good than the existing systems.
I don't think there are any generic issues related to the elevated SFP design used in these BWRs. In fact, it has some significant advantages in terms of ALARA implementation during refueling. Procedurally, yes, you could address some of the concerns by limiting SPF inventory during a full-core offload.
I suggest simple materials handling solutions that move the spent fuel, that not in the immediate process of being unloaded, off too a more secure part of the facility. For a hundred or so years we have been moving material in devices like this. We surely can build a transport for very hot rad waste.