I'm a bit more worried about the security aspect of it.

Let's say that we are running a server on a port which uses this option to allow multiple processes to bind to it. What's to prevent a rogue process, perhaps with malicious intent, from starting up and siphoning off requests willy nilly? Sounds like a great way to implement a hard to detect MITM attack.

What would be nicer, I think, is if socket reusing was bound not only to the same uid but also to the process listening to it.