You mean that you don’t want a single user to have more than 3 accounts? It’s trivial to go to a coffee shop to get a new IP (and there are a zillion other ways to get a different IP while at home in your pajamas if someone wants to bother to try).
I’d say that you’re going to have to enforce this with community rules rather than technology.
Of course I only realized this was Contribute > Feature and not Support after I’d writtten the whole message, or I’d not said anything. 