I think you can already, with the ip2name option, if i remember correctly.
It would be nice indeed to have a whois for the ip, but indeed it would consume much time and doesn't work that easy.
But, if you have given certain users access, than you have their ip to convert.
In case you give public access, then sniffing on ip and backtracing could be a privacy violation and users who use proxies are more or less untraceble anyway. You are allowed to log, but should respect the privacy of your visitors.