I thought it was pretty clear, but the proposal is to close accounts that receive a significant number of mixed coins. That "significant" part is important -- i

I thought it was pretty clear, but the proposal is to close accounts that receive a significant number of mixed coins. That "significant" part is important -- it varies per account. Obviously it needs to be high enough to fend off trolling, but low enough to fend off laundering. That's not a difficult proposition; it's equivalent to fraud detection that credit card companies employ.