We'd also need to limit it to connected UDP then which both adds complications, if not an extra server call. But I hope we might rely on the sockets not giving ECONNREFUSED for send() in any other cases, error codes are documented and breaking those in Unix kernel will probably break a lot of things anyway.
I've never managed to find more than vague documentation for any error handling when it comes to sockets; do you have a better source?
I'll admit "breaking those will probably break a lot of things" is not a particularly comforting thought. At this point I'm pretty well convinced that nobody really knows how to handle network error conditions, and that's why network software is universally so bad...
I'm not too scared to sign off on this patch, but it's something that we'll have to watch out for.