Just accept that the cost of changing from the existing 'intermodal' shipping container as an OUTSIDE standard when on the ocean is too high.

Having a light weight inner unit, maybe something like a pallet sub-unit or dimension-ed around being pallet compatible but expecting a long run to be conveyed out quickly, then loaded in to something else quickly would be a better place to begin from.

Then you'd only need to figure out a good boxing solution for THAT on an existing trucking platform. Re-using the same intermodal locking interface for existing trailers but with a lighter build on top could be useful, particularly if the re-packing allows for a full container load to just go somewhere.

However since unpacking is happening, automated pallet handling/routing might also be a useful economic goal since there would then be an opportunity to sort and re-pack/re-mix at the dock-side.