Suggestion for Chat RMT advertising fix

I can't imagine a perfect solution to get rid of all chatbots but here's my idea, along with some thought on why it can work to an extent. (I hope the implementation isn't some headache)

Problem:
Bot accounts spamming chat with RMT websites or other nonsense.

Idea:
Option to hide messages from users that have not reached a determined threshold of challenges completed in league.

Implementation:
Checkbox or number box on "UI" settings under "Chat" options. It hides any messages from accounts under the determined amount.

Theorized Results:
Reduction in perceived amount of bots in chat.
New characters can't message early in game.

Observations:
Threshold should be low enough to not allow elitism. IE, 40/40 players only chatting with 40/40 players.
Option should be defaulted to be off and not filter messages, once the league progresses, players will be able to decide when to turn it on and avoid RMT bots.
Threshold could also be determined by other progression metrics like gold earned, specific missions, act completion etc.

Thank you for your time

This may come across as slightly blunt, but the most effective anti-bot solution would likely be a simple threshold, say a $20 minimum spend. Genuine, active players, or anyone intending to participate in chat would have easily surpassed this threshold. Bots, on the other hand, would be severely impacted, as each banned account would cost them $20 to replace just to continue chatting.

Yeah, I'd say forcing people to pay is too much because it's a free game. I imagine a good way to do it is use metrics tied to time and not money.