This won't happen. There is a strong anti-censorship attitude among witnesses and the creator of these accounts can simply create more and more. They would have to implement an expansible centralised spam list that would disable any commenter that the witnesses don't like. This would be dangerous for the ability of people to express themselves freely and is something that the witnesses have talked about and rejected.

If it will be reconsidered in the future, maybe in the far far future, but for now this is not an option.

For now, our best solution is in the front ends. Mute and downvote and let the front ends hide the comments.

There is already a set of centralised spam lists, since 2018, which is themarkymark's buildawhale spam list. Many people already complain about it but it's not applied directly to the blockchain but to front ends. If someone is in that list, they simply don't show up in the comments' section when they comment, although they are indeed registered in the blockchain.