Not a bad idea, but how would the system detect someone who accesses the forum using Tor browsers or a VPN that does not store a user's browsing log or history? How would the proposed system identify such people?
Not always changing the IP address can serve as a reassurance to the user that he is unique.
You can look at these articles, which say that in addition to changing the IP, there are still a lot of ways in which you can track a person and talk about their uniqueness. By changing the IP accordingly, everything related to the user's system will remain unchanged, and sites that have anti-fraud protection installed will very easily see their unique users, even if they try to change their IP. And those who use TOR immediately have a negative attitude.
There are a lot of trackers that are almost impossible for a simple user to change without additional equipment and knowledge.
https://webkay.robinlinus.com/https://coveryourtracks.eff.org/