Well, even if IP restrictions are placed, scammers will just use VPN or other devices. The way to stop the spam is to regulate the bounty section and make certain regulations like the amount of persons who can participate in the campaign, and ranks. Many bounties accept totally new accounts for their campaigns on social media which leads the spammers to create new accounts. If there's a bar placed like "minimum member rank" then it can be stopped to a great extent.
If the forum had decided to have unique users, namely, would have introduced a ban on the registration of alternative accounts, then it would not have been necessary to identify users only by their IP address.
Already today, many sites and forums use the Fingerprint JS and Browser Fingerprint analytics system. Owners want to know how many first-time visitors they have on their site and how many regular users.
But everything has been discussed many times, and the privileges that are given on this forum, in terms of the ability to have multiple accounts, are not always used in the right way.
Once again, the introduction of the Fingerprint analytics system would instantly weed out all other alternative accounts. And only then it would be possible to have a more or less real number of users.
https://fingerprintjs.com/
Will the use of fingerprint will expose the identity of the people ? The least thing anyone would want is the KYC on this forum. Perhaps there may be ways to identify alt accounts other than KYC.
Bitcointalk is the most popular forum and three million accounts is still a small number considering the total population of the world.