There really needs to be an option that users can turn on to block all @ from people they don't follow. Even temporarily, say for a period of a month at a time.

I'm also a fan of the "reddit gold" style idea of cheap paid accounts that don't necessarily have to be paid by the account holder. That would make it easy to allow people to filter out unpaid unknown accounts and raise the cost of abuse.

The underlying problem is that comment moderation is a kind of emotional labour that can be fairly gruelling at times, and it needs suitably paid staff to do. Attempts at automatically dealing with it are very much like the early days of spam fighting: not very accurate and constantly shifting. But whereas spam is broadcast, abuse is targeted.