First, with regional ISP, the IPs usually clustered in blocks.
Secondly, with the aforementioned API you can get the ISP, the city, and the postal code. Hence, if a user been banned, and in a few days someone opens a new account with the same parameters, pretty sure it's the same banned user. Of course, if the user base was millions of people, it would not work well, but with the current numbers there will be very few false positives, if any.
quote: their elo stay the same ... it will not impact the balance |
Balance isn't the only problem. The fact that they were banned indicates that they break the rules, exhibit behavior not suited for this game and this community, and that your suggestion doesn't solve.