I've read some detailed discussions from people in the industry explaining how blockchains don't help. And I've read some very high level, breezy assertions from people outside the industry asserting that blockchains can help (although they never spell out how, exactly).
As far as I can tell:
1. There's a pretty big issue with containers having the wrong contents (eg, counterfeit items loaded initially, or contraband added during transit). Current solutions are focused around physical security, seals, locks, etc., but it's fairly easy to bypass and forge these physical measures.
2. There's no real issue with tracking containers. We don't always know what's actually in them, but we know really well where they are and what's meant to be in them.
3. There's some efforts to try and replace the electronic systems for tracking where they are and what should be in them with blockchains. But as above, that's the bit that's currently working fine.
Not needing to trust middlemen is a good goal, I just don't see how tracking containers on blockchains reduces my need to trust middlemen. When Customs seizes the container at the border and finds someone has added 100kg of cocaine to the container, how does the blockchain prove who jimmied the lock open and then replaced the tamper seals?