Thank you very much for this detailed comparison.

I must say that while supporting your full interface looks like a lot more work, since it is designed to be extensible, it should be possible to make a compatible subset that, as you say, can be extended without requiring the core API to change.

I certainly support your choice of using Schemely names instead of Unix-specific, all-caps names like SOCK_STREAM; of making it possible to use the same interface to support things like Unix domain sockets and other implementation-specific types; and not requiring that a separate socket be allocated for each recipient address for UDP packets.