Allowing stacking over 2 high is only useful if you have the equipment to stack over 2 high. A place that just stacks empty containers 2 high probably only has large forklifts. The special equipment for high stacking is far more expensive, and only bought if you need it.[2]
A more useful proposal is a "peel pile".[3] This is a system which assigns outgoing trucks an easily accessible container to deliver, rather than a specific container that has to be retrieved. There's an app for that. This is being implemented by IMC, the largest marine drayage company in the US. They say they're already up to 8 high stacks in the LA area. The higher the stack, the longer the retrieval time.
"This keeps drivers moving and productive, even if they don’t know the exact load they’re getting or the delivery location." So it's really dumping the sorting problem on drivers. They have no idea where they're going next. There has to be some way to separate containers by approximate location to make this work, so a driver knows how far they're going to be asked to take the thing.
How well this all works depends on how well the software organizing the stacking works.
[1] https://jalopnik.com/the-streets-of-los-angeles-are-overflow...
[2] https://www.bison-jacks.com/why-bison/blog/how-to-lift-a-shi...