They've been testing it in Receive Centers in multiple DCs for a few years. They call them cab cubes. Its improves ship load accuracy. Every item picked is loaded and attached to its own specific cab cube which are each then attached to the MCL.
The cab cubes are then double stacked in the trailer and either go straight to a receive center to be broken down and shipped to smaller city stores, or straight to the smaller stores themselves, which need fast unloads because of trailer parking constraints in major cities. A full trailer can be unloaded in like 30 minutes.
The pull to ship process in the DC is longer but the accuracy of shipments is way higher, like 97% or something ridiculous and anything that's not on the appt gets swept back to the DCs. This was suppose to the future of all target shipments but hasn't made it that far.