Might as well go big. 24 extra bytes per packet is not that big deal. And having that much extra space means you can screw up design multiple times and still be able to reuse lot of infra. Also getting rid of idea that you are even trying to manually manage the address space eases many things.

But it's not human readable anymore, nor backwards compatible. The expectation was that the industry is reasonable, but it proved to be as hard as it would be to push breaking email v2 implementation.