Techies tend to look for technological solutions for problems, but IMHO this is rather a social one.

Though discussing an identifier per IP may be worth it in general, I'm sceptique here.

IMHO evolutionary pressure will only push abuse into other patterns, like VPN tunnels or throw away accounts.

So please forgive me if I'm not deepening this discussion any further.

For me it's just another variant of feeding in this asymmetric war. :)