Totally agree, I'm always wanting to see who's visiting my site and where from, especially if google is crawling my site, and I'm unable to decipher what's a robot and what's not. So the IP's would need to resolve to a host.
As things stand we cannot see the IP address a post comes from, not the IP addresses in Who's Online. I don't know how others manage their sites, but in all my years of managing communities I could never contemplate the idea that you have some troublemaker on your site and yet you can't find the IP they're coming from.
So please, I would implore Mike and Kier to add this as soon as possible. It's essential. Both in posts and Who's Online.