Not sure if there is a feature like this out there, but it would be nice if there was an option where I could select a specific IP address, and something logs every time that ip address comes to the forum.
Let's say I banned a member, I think it would be useful to know how often they are visiting as a guest.
This definitely sounds like an addon kind of feature rather than a core feature. Sounds like you want to spy on an IP. I think you can do this with a little bit of effort already, but this isn't really necessary to be in the core.