Reverse voltage protection and high-side current switch
It seems to me that in the datasheet of the ITS428L2, reverse battery protection only means that the switch will not be destroyed in case of wrong polarity (see on page 8).

Concerning your circuit: even if it protects against reverse battery, you can never switch off the load because regardless of the MOSFET's gate potential the body diodes will always conduct (given that the battery is connected in correct polarity).

When it comes to the direction ID in a MOSFET datasheet you have to pay attention to the mode of operation. If the gate is driven, the channel is  defined by the RDSon. Here the direction of the current doesn't matter, as you correctly said. But suppose an inductive load is driving a current through the body diode into the battery when the MOSFET is off. The body diode is a much lossier conductor that a fully turned on channel and therefore the permissive current is significantly less.