Right, but that wasn't the question. Having done a lot of work with genetic algorithms, among other things, I have no doubt that I could sit down and write a reasonably useful solution. However, it would be absolutely brilliant if this was already part of an existing shipping API.

I think it would be very useful if these shipping API's accepted package specifications and helped optimize final packaging while in the process of providing a quote. If you want to talk about differentiating a solution, this, most definitely, would.

It may be infeasible at massive scale, but many systems do it right now with approximation algorithms, heuristics, and integer programming. Fedex, Walmart, Amazon, and most other industrial or logistics corporations have teams of people with a background in discrete optimization or operations research building and improving similar systems.

I'm not aware of any public APIs for this at present.