One of the reasons comments are so tempting is they are free. There's little risk of downvotes or upvotes, and folks often use them for things they're not meant for.
A few proposals I've heard have been about limiting comments per day or actually adding a reputation cost.
Been considering an alternate approach - we want folks to clean up after themselves, and prioritise what comments they want to keep - and having a finite number of comments, sitewide would encourage users to clean up after themselves.
There are a potentially few nice additions here. It's an invisible cost - and with a sufficiently high number, many users might not notice. When you run out of comments, either you think about it harder, or go back and delete old comments. You can also adjust it - with penalties on overall comment count for accepted negative flags or increases for say higher reputation.
It gives people the freedom to post transient comments as needed, and gives them an enticement to remove them once done.
And there's a certain poetry in restricting the total number of comments, over other means to deal with accepted R/A flags. It also leaves some room for tweaking, if we felt it was too restrictive.
One issue I forsee is folks may suddenly find they hit the limit, which would be bad, and probably require some assistance for them to clean up but with a high enough limit, it might be less of an issue.
On the other hand, it implicitly forces users to decide on the value of their past comments.