True I have not seen any on the Gen4 either.I have not seen a true LS offered on the Gen 4 Expedition, only the electronic model. If there was a true LSD that would be news to me.
I think we are getting to caught up in the Limited Slip which is OLD tech per say. I have a Ford Van with Non Limited Slip but it does have the Advance Trac which uses a non limited slip diff and applys brake to the spinning wheel. It works remarkably well I got caught in snow in Flagstaff with summer tires and it handled excellet. I was surprised.